In order to make the simulation model closer to physical prototype, mechanical hydraulic coupling simulation model on axial piston hydraulic motor was established, and the factors including the friction force of cylinder plunger and cylinder block, cylinder plunger and swash plate, the viscous damping of fluid and the triangle damping groove which is to decrease the pressure fluctuation were taken into consideration. Through the high pressure oil of the hydraulic motor pushing plunger to move and mechanical energy driving plunger to discharge oil, the mutual conversion between hydraulic energy and mechanical energy was implemented. The simulation model mainly included the pressure source (constant current source or constant voltage source )，load (external resistance moment), piston and cylinder components, reciprocating and rotating motion transformation components of the plunger, oildistribution port, etc. In the model, cylinder was connected with rigid or elastic locking device. Piston and cylinder surface is simplified to a springdamper elastic sealing unit. In order to realize positive inversion of the hydraulic motor, triangle unloading groove was set in the both ends of the oil inlet and outlet of the valve plate. Through the contrast between simulation result and experimental data from literature, it can be found that the errors of motor speed, acceleration time and maximum flow output are less than 5%. The accuracy of simulation model was testified. According to the simulation result, on account of the flow area mutation of the unloading groove and the waist type slot transitional region, there is a local pressure pulse; and the higher rotational speed is, the greater pressure fluctuation is. The pulsating pressure could be alleviated through improvement of structure and optimization of parameters of the load discharging groove. The performance characteristic of hydraulic motor will be affected by load, when the moment of inertia of load is high, the acceleration time will be long, the fluctuating region of steady rotational speed will be narrow, and the corresponding impulse will be smaller.