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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-08-03</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000863456</issuerCik>
        <issuerName>WET SEAL INC</issuerName>
        <issuerTradingSymbol>WTSLA</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001413003</rptOwnerCik>
            <rptOwnerName>Steven Benrubi</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>26972 BURBANK</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>FOOTHILL RANCH</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>92610</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Exec. VP &amp; Chief Fin. Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock Class A</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2010-08-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>90000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.33</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>186870</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Non-Qualified Stock Option (right to buy)</value>
                <footnoteId id="F2"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>3.44</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-08-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>90000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>3.44</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-08-03</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>90000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>208870</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On August 3, 2010 restricted stock was granted pursuant to The Wet Seal, Inc. 2005 Stock Incentive Plan. The restricted stock will become vested with respect to 33 1/3% of the shares on each of the next three (3) anniversaries of the Date of Grant until the restricted stock is 100% vested, subject to Executive's Continuous Service with the Company on each of those vested dates.</footnote>
        <footnote id="F2">On August 3, 2010 stock option were granted pursuant to The Wet Seal, Inc. 2005 Stock Incentive Plan. The options will become vested and exercisable with respect to 33 1/3% of the shares on each of the next three (3) anniversaries of the Date of Grant until the options are 100% vested, subject to Executive's Continuous Service with the Company on each of those vesting dates.</footnote>
        <footnote id="F3">The stock options become exercisable in three (3) equal annual installments of the first, second and third anniversaries of the grant date thereof.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Steven H. Benrubi</signatureName>
        <signatureDate>2010-08-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
