Aimed at the parameter uncertainties and extra torque in passive force control system,an adaptive backstepping controller is proposed based on the established nonlinear model of the system.The stability of the controller is testified by the Lyapunov stability theory,in which the parameter uncertainties and extra torque are considered.The nonlinear model of the system is established to construct several new virtual subsystems,then the backstepping thought is introduced to the design of the dummy controllers for each dummy subsystem.By backstepping recurrence,the nonlinear controller with parameter uncertainties and disturbance of load bearing system is obtained.The result of simulation shows that the designed controller can eliminate extra torque better compared with traditional controller,which proves the effectiveness of the proposed approach.