Fitting model function with load inertia, viscous damping coefficient, load gravity torque and load initial position angle as parameters to be identified is established through the motor kinematics equation. The four parameters are fitted by the nonlinear regression method based on the model function, and the noninertia load torque is obtained. Adding the load torque to the current loop in the classical motor PI control method as the feed forward compensation to realize the compensation of time-varying load torque. The simulation results show that this method can enable the control system to respond quickly to input speed commands, and avoid the appearance of large speed error.