This　study　systematically　investigates　the　influence　of　the　time-varying　friction　under　mixed　elastohydrodynamic　lubrication　(EHL)　on　the　dynamic　response　of　S-type　profile　herringbone　gears　through　theoretical　modeling　and　numerical　simulation.　A　high-precision　3D　mesh　model　is　constructed　based　on　the　tooth　profile　and　meshing　line　equations.　The　time-varying　meshing　stiffness　(TVMS)　is　obtained　through　finite　element　analysis　and　the　relative　sliding　and　coiling　velocities　are　determined.　Considering　nonlinear　factors　such　as　TVMS,　tooth　side　backlash　and　comprehensive　meshing　errors,　an　ordinary　dynamic　model　is　established　to　calculate　the　initial　dynamic　meshing　force　(DMF).　The　friction　under　mixed　EHL　is　then　introduced,　and　a　dynamic　model　incorporating　friction　is　coupled　with　the　mixed　EHL　model　for　iterative　solving　of　the　time-varying　friction.　Through　numerical　simulation,　the　variations　of　the　friction　coefficient　under　different　operating　conditions　and　its　influence　on　the　dynamic　response　of　the　gear　system　are　explored.　The　results　indicate　that　the　S-type　profile　herringbone　gear　exhibits　lower　vibration　amplitudes　compared　to　the　conventional　involute　gear　under　identical　conditions.　Furthermore,　friction　significantly　affects　not　only　the　vibration　amplitude　but　also　the　frequency-domain　characteristics　and　dynamic　stability　of　the　S-type　herringbone　gear　system.　Notably,　within　high-frequency　ranges,　the　presence　of　friction　causes　the　system　to　enter　chaos　earlier,　while　simultaneously　suppressing　chaotic　motion.