Parameters tuning of robot joint motor′s controller was the key of good control performance realization. A parameter tuning method was presented for joint motor sliding mode control based on alternating simultaneous iteration. Firstly, the permanent magnet synchronous joint motor was designed, and the control object of the system was determined. Secondly, the slidingmodePID control system that combined the PID current controller with the sliding mode speed controller was designed. The sliding mode controller′s parameters were set initially using engineering design methods. A redundant PID speed controller was added and its parameters were also set by engineering design methods. Using the output speed of the redundant PID speed controller and sliding mode speed controller as iterating variable, the parameters of controller were obtained via alternating simultaneous iteration. Finally, it was proved by the MATLAB/Simulink simulation that the proposed method was effective and feasible.