The　existing　gear　dynamics　models,　when　dealing　with　the　effect　of　gear　error　on　gear　dynamics,　always　omit　distinguishing　one　pair　of　teeth　from　two　pairs　of　teeth　in　contact　during　gear　transmission　since　the　contact　ratio　of　gears　is　greater　than　one.　Therefore,　these　models　are　unable　to　indicate　the　overall　real　conditions.　Based　on　the　concept　of　gear　pair　integrated　error　(GPIE)　is　proposed　a　new　comprehensive　dynamics　model　for　spur　gear　pair,　taking　into　account　the　number　of　teeth　in　contact,　is　built　to　overcome　the　drawbacks　of　existing　models.　Meanwhile,　the　nonlinear　factors　such　as　gear　errors,　time-varying　mesh　stiffness　and　load　sharing　are　considered　in　the　new　model.　Critically,　the　GPIE　has　the　advantage　to　identify　the　number　of　teeth　in　contact　in　the　whole　gear　rotation　process,　thus　overcoming　the　limitations　in　conventional　gear　dynamics　models.　According　to　the　actual　GPIE　curve　from　a　gear　integrated　error　tester,　the　simulations　of　a　gear　pair　under　various　working　conditions　are　conducted　by　the　new　model,　and　the　gear　dynamic　behaviors　are　analyzed.　The　research　results　clarify　some　phenomena　related　to　gear　transmission,　and　can　be　used　in　dynamics　design　and　noise　control　of　gears.　©　2010　Journal　of　Mechanical　Engineering.