The wear failure is easy to be produced on the surface of eccentric shaft around the critical speed for a certain type of telescopic cylinder hydraulic motor,which affects the performance and service life of the hydraulic motor.To study the wear failure mechanism of telescopic cylinder hydraulic motor,the dynamical model of ecentric shaft and singlecylinder was established,and the force analysis of cylinder under dynamic was performed.Through Matlab simulation verifies that,when inertial force caused by negative acceleration of cylinder exceeds the composite force of sprin〖JP2〗g’s〖JP〗 elasticity,external load and cylinder weight,the cylinder will separate from the surface of eccentric shaft,thus causing a “wreath” shock and vibration.This research verifies that hydraulic motor has the possibility of an impact vibration and wear around the critical speed.