In the pump-control-motor hydraulic system,due to the sudden change of external load,the engine speed will change,which will lead to the change of the variable pump speed,and eventually the hydraulic motor speed fluctuation is too large and the adjustment time is too long.Aiming at the closed hydraulic system of variable pump and fixed motor,the mathematical model was constructed in detail,the block diagram of transfer function was obtained,and the reasons for the fluctuation of motor speed due to load change were analyzed.A feedforward compensation control method was proposed,which could compensate the flow change caused by the speed disturbance of the variable pump by changing the swash plate swing angle of the variable pump in real time.The compensation function was deduced,and the simulation analysis was carried out for step 100% load,step 20% load condition and ramp 100% load,ramp 20% load condition.The results show that the motor speed fluctuation with feedforward compensation control is reduced by 3.87% at most,and the adjustment time is shortened by at most 1.77 s.