Based on multirate output feedback control law and region pole assignment technology,a discrete sliding mode control algorithm is presented. The control law is adapted to seeker servo system,which is disturbed by friction,coupling and restriction moment. The method to determine the parameters of the controller is also given. The disturbance doesn’t need to satisfy the match condition and the boundary of the disturbance is known. Theoretical analyses show that the control strategy can guarantee the stability of the closed loop system. This methodology doesn’t need the system states for feedback as it makes use of only the output samples to design the controller. Thus,it is more practical and easier to be implemented. Simulation results show that by adapting the presented control law,the servo system of seeker can reach good performance in the presence of disturbance. The advantages,such as easy implementation and good dynamic performance,make the control law more promising on control system design of seeker.