Profile　of　the　path　of　contact　(PPC),　as　a　characteristic　curve　on　the　gear　tooth　surface,　is　with　specific　engineering　significance.　It　can　reflect　the　quality　of　gear　machining　and　gear　transmission.　The　PPC　is　not　only　the　generative　curve　in　gear　hobbing,　worm　grinding　and　other　generative　machining,　but　also　the　working　curve　in　the　involute　gear　transmission.　However,　there　is　no　function　to　measure　the　deviation　of　PPC　for　the　existing　gear　measuring　instruments.　The　theoretical　model　of　the　PPC　is　presented,　which　is　based　on　the　gear　geometry.　By　means　of　the　existing　gear　measuring　center,　the　four-coordinate　method　and　the　three-coordinate　method　for　measuring　the　deviation　of　PPC　are　proposed.　The　measurement　practice　indicates　that　the　measurement　and　evaluation　of　the　PPC　can　be　realized　by　using　the　existing　gear　measuring　instruments.　The　form　deviation,　slope　deviation　and　total　deviation　of　the　PPC　measured　by　the　four-coordinate　method　are　0.　2,　1.　3,　and　0.　6　μm,　which　are　different　from　those　measured　by　the　three-coordinate　method.　Compared　with　the　gear　involute　and　helix,　the　PPC　has　features　of　comprehensiveness,　unity,　and　uniqueness.　The　optimal　deviation　of　PPC　is　obtained　through　synthesizing　the　involute　deviation　and　helix　deviation　of　the　gear,　which　effectively　reduces　accuracy　requirements　for　the　gear　involute　and　helix.　©　2023　Science　Press.　All　rights　reserved.