Aiming at the extra torque of passive force control system,a total state feedback controller is proposed based on backstepping theory.And the stability of the controller is ensured by Lyapunov stability theory.The proposed method employs the parameters of loading system as well as the parameters of load bearing system to differ from the previous methods for dealing with extra torque.A nonlinear model of the system is established to construct the new virtual subsystems,then the backstepping theory is introduced to design the dummy controllers for each dummy subsystem,the nonlinear controller containing all states of loading system and load bearing system is transposed to restrain the extra torque step by step.The simulated results illustrate the effectiveness of the developed controller.