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

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-04-15</periodOfReport>

    <issuer>
        <issuerCik>0001061630</issuerCik>
        <issuerName>CAPITAL TRUST INC</issuerName>
        <issuerTradingSymbol>CT</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001177127</rptOwnerCik>
            <rptOwnerName>NASSAU HENRY N</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O INTERNET CAPITAL GROUP, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>600 BUILDING, 435 DEVON PARK DRIVE</rptOwnerStreet2>
            <rptOwnerCity>WAYNE,</rptOwnerCity>
            <rptOwnerState>PA</rptOwnerState>
            <rptOwnerZipCode>19087</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock Units</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
            </securityTitle>
            <transactionDate>
                <value>2004-04-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>26</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F3"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1377</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">The Reporting Person directly beneficially owns 9,600 shares of Class A Common Stock.</footnote>
        <footnote id="F2">The Reporting Person indirectly beneficially owns 400 shares of Class A Common Stock held by his two sons.</footnote>
        <footnote id="F3">Represents Class A Common Stock Units credited to the account of the Reporting Person which convert to shares of Class A Common Stock on a one-for-one basis.  The number of shares of Class A Common Stock subject to the Class A Common Stock Units credited to the Reporting Person was determined by dividing (1) the product of the number of shares of Class A Common Stock subject to all Class A Common Stock Units held by the Reporting Person and the per share dollar amount of the Class A Common Stock dividend paid by the Company on April 15, 2004 by (2) the closing price of the Class A Common Stock on the New York Stock Exchange on April 15, 2004.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Brian H. Oswald, on behalf of Henry N. Nassau</signatureName>
        <signatureDate>2004-04-16</signatureDate>
    </ownerSignature>
</ownershipDocument>

