Tooth　surface　material　loss　caused　by　gear　wear　alters　the　surface　morphology　of　gears,　which　impacts　their　vibration,　noise,　and　remaining　lifespan.　Although　gear　wear　modeling　and　prediction　have　been　extensively　studied,　this　paper　proposes　a　novel　approach　based　on　the　theorem　of　degradation　entropy　generation　(DEG).　A　point-by-point　calculation　method　is　introduced　to　determine　the　degradation　coefficient　for　each　measurement　point　on　the　tooth　profile,　accounting　for　varying　working　conditions　along　the　tooth　profile　during　the　actual　meshing　process　of　the　gear　pair.　First,　the　FZG　gear＇s　bearing　capacity　is　tested.　Next,　a　surface　roughness　profilometer　is　employed　to　in-situ　measure　the　tooth　profile　after　each　load　stage.　The　profile　deviation　curve　and　the　amount　of　profile　wear　following　each　load　stage　are　obtained　by　processing　the　measured　profile　morphology　data.　Then,　the　pitting　safety　factor　for　each　point　on　the　tooth　surface　is　calculated　according　to　the　ISO　6336-22:2018　standard　and　used　to　correct　the　degradation　coefficient　for　that　point.　Finally,　the　entropy　generation　of　the　system　during　each　load　stage　of　the　FZG　gear　is　calculated.　The　degradation　coefficient　suggested　in　the　DEG　theorem　is　employed　to　link　gear　wear　with　system　entropy　generation,　realizing　gear　wear　modeling　and　prediction.　The　results　demonstrate　that　the　gear　wear　calculation　method　based　on　the　DEG　theorem　can　accurately　predict　the　evolution　of　tooth　profile　surface　morphology　during　the　experimental　process.　This　research　provides　a　unified　calculation　method　for　surface　morphology　evolution　caused　by　gear　wear　during　service.