As　the　most　widely　used　gear　measuring　instrument,　the　gear　measuring　center　can　measure　the　individual　deviations　of　a　gear　tooth　flank　other　than　the　comprehensive　deviations　of　the　gear.　However,　gear　transmission　error　is　an　important　transmission　performance　indicator　in　the　gear　meshing　process.　It　is　an　important　trend　of　gear　measuring　to　obtain　the　transmission　error　from　individual　deviations.　In　this　study,　a　calculation　method　of　gear　transmission　error　is　proposed　based　on　the　point　clouds　of　the　gear　obtained　by　optical　sensors.　According　to　the　gear　meshing　principle,　a　method　is　introduced　to　determine　the　contact　status　between　the　tooth　flanks　formed　by　the　point　clouds.　According　to　this　introduced　method,　the　single　tooth　pair　meshing　process　and　the　meshing　process　of　multiple　tooth　pairs　are　analyzed　to　determine　the　gear　transmission　error　curve.　The　comparison　results　of　tooth　contact　analysis　and　gear　measurement　experiments　verify　the　proposed　virtual　measurement　method.