Abstract: This paper analyzes the influence of mechanical clearance error on the displacement, load pressure and flow rate of the hydraulic cylinder of the servo loading system. The compensation control method of the mechanical clearance error of the servo loading system is then proposed. In addition, a nonlinear model of the servo loading system under the influence of the mechanical clearance error is established. Finally, the Simulink simulation and system experiments are implemented to verify the accuracy of the nonlinear model of the servo loading system and the mechanical clearance compensation method.It can be seen from the experimental results that the accuracy error of the output load force reduces from 18% to 10% under low speed and small load conditions, and from 21% to 8% under high speed and large load conditions. The hysteresis error of the output load force of the servo mechanism of the tested products in the whole stroke is basically eliminated.