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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-08-07</periodOfReport>

    <issuer>
        <issuerCik>0000009984</issuerCik>
        <issuerName>BARNES GROUP INC</issuerName>
        <issuerTradingSymbol>B</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001307654</rptOwnerCik>
            <rptOwnerName>Dempsey Patrick</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>BARNES GROUP INC.</rptOwnerStreet1>
            <rptOwnerStreet2>123 MAIN STREET</rptOwnerStreet2>
            <rptOwnerCity>BRISTOL</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06010</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-08-07</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>.158</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>33.78</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>243864</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-08-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1152</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>34.17</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>242712</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-08-09</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>956</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>34.17</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>241756</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4109.55</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Company's 401(k) Plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes balances of 3929 Restricted Stock Units granted 2/9/2011, 4733 granted 2/8/2012, 8200 granted 2/12/2013, 13600 granted 3/1/2013, 16200 granted 2/12/2014 and 3100 granted 2/12/2014, and 11800 Performance Share Awards granted 2/8/2012, 13700 granted 2/12/2013, 22600 granted 3/1/2013, 27000 granted 2/12/2014 and 5100 granted 2/12/2014, that are subject to forfeiture if certain events occur.</footnote>
        <footnote id="F2">Includes balances of 3929 Restricted Stock Units granted 2/9/2011, 2366 granted 2/8/2012, 8200 granted 2/12/2013, 13600 granted 3/1/2013, 16200 granted 2/12/2014 and 3100 granted 2/12/2014, and 11800 Performance Share Awards granted 2/8/2012, 13700 granted 2/12/2013, 22600 granted 3/1/2013, 27000 granted 2/12/2014 and 5100 granted 2/12/2014, that are subject to forfeiture if certain events occur.</footnote>
        <footnote id="F3">Includes balances of 1964 Restricted Stock Units granted 2/9/2011, 2366 granted 2/8/2012, 8200 granted 2/12/2013, 13600 granted 3/1/2013, 16200 granted 2/12/2014 and 3100 granted 2/12/2014, and 11800 Performance Share Awards granted 2/8/2012, 13700 granted 2/12/2013, 22600 granted 3/1/2013, 27000 granted 2/12/2014 and 5100 granted 2/12/2014, that are subject to forfeiture if certain events occur.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Monique B. Marchetti, pursuant to Power of Attorney</signatureName>
        <signatureDate>2014-08-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
