<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-05-07</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001540947</issuerCik>
        <issuerName>EQT Midstream Partners, LP</issuerName>
        <issuerTradingSymbol>EQM</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0000033213</rptOwnerCik>
            <rptOwnerName>EQT Corp</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>625 LIBERTY AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 1700</rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15222</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Director by deputization</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001552976</rptOwnerCik>
            <rptOwnerName>EQT Midstream Investments, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>625 LIBERTY AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15222</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Director by deputization</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001552977</rptOwnerCik>
            <rptOwnerName>EQT Investments Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>101 CONVENTION CENTER DRIVE, SUITE 850</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LAS VEGAS</rptOwnerCity>
            <rptOwnerState>NV</rptOwnerState>
            <rptOwnerZipCode>89109</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Director by deputization</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001607430</rptOwnerCik>
            <rptOwnerName>EQT Production Co</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>625 LIBERTY AVENUE, SUITE 1700</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15222</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Director by deputization</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001607404</rptOwnerCik>
            <rptOwnerName>EQT Gathering Holdings, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>625 LIBERTY AVENUE, SUITE 1700</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15222</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Director by deputization</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001607403</rptOwnerCik>
            <rptOwnerName>EQT Gathering, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>625 LIBERTY AVENUE, SUITE 1700</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>PITTSBURGH</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>15222</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Director by deputization</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Units</value>
            </securityTitle>
            <transactionDate>
                <value>2014-05-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>516050</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3959952</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This Form 4 is being filed jointly by EQT Corporation (EQT), EQT Midstream Investments, LLC (Midstream Investments), EQT Investments Holdings, LLC (Investments Holdings), EQT Production Company (EQT Production), EQT Gathering Holdings, LLC (Gathering Holdings) and EQT Gathering, LLC (EQT Gathering) in connection with the sale of certain midstream assets by EQT to EQT Midstream Partners, LP (Issuer) pursuant to that certain Contribution Agreement by and among the Issuer, EQT Midstream Services, LLC, (General Partner), EQM Gathering Opco, LLC and EQT Gathering, dated April 30, 2014, in which the Issuer acquired certain midstream assets for aggregate consideration of approximately $1.18 billion, consisting of (i) a $1.12 billion cash payment, (ii) 516,050 common units of the Issuer issued to Midstream Investments and (iii) 262,828 general partner units of the Issuer issued to the General Partner.</footnote>
        <footnote id="F2">The common units of the Issuer are owned directly by Midstream Investments. EQT directly owns 100% of the outstanding membership interests of Investments Holdings.  Investments Holdings directly owns 100% of the common stock of EQT Production. EQT Production owns 100% of the membership interests of Gathering Holdings. Gathering Holdings owns 100% of the membership interests of EQT Gathering. EQT Gathering directly owns 100% of the membership interests of Midstream Investments. EQT, Investments Holdings, EQT Production, Gathering Holdings and EQT Gathering  may therefore be deemed to beneficially own common units of the Issuer owned directly by Midstream Investments.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Philip P. Conti, Senior Vice President and CFO of EQT Corporation</signatureName>
        <signatureDate>2014-05-07</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Randall L. Crawford, President of EQT Gathering, LLC, the sole member of EQT Midstream Investments, LLC</signatureName>
        <signatureDate>2014-05-07</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Joshua C. Miller, Vice President of EQT Investments Holdings, LLC</signatureName>
        <signatureDate>2014-05-07</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Steven T. Schlotterbeck, President of EQT Production Company</signatureName>
        <signatureDate>2014-05-07</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Randall L. Crawford, President of EQT Gathering, LLC</signatureName>
        <signatureDate>2014-05-07</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ Randall L. Crawford, President of EQT Gathering Holdings, LLC</signatureName>
        <signatureDate>2014-05-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
