Dynamic model of gear system is established with the consideration of gear manufacture error

installation error and external load.Then

according to the process of meshing process which may arise meshing impact

separation and tooth surface collisions

the dynamic equation with state coefficient is set up

and the phase path of gear mesh process is qualitatively in state space.The results show that the mechanism of clearance which arouse by gear error and gear separation during meshing process and the reasons of chaotic.Finally

taking tooth mesh period as calculation unit to achieve numerical calculation of meshing process and verified by example.The results of example give the interpretation why the gear system to produce a large noise and overlap ratio less than the theoretical value.