Considering the characteristics of servo system, a robust-optimal control method to deal with object's uncertainty and disturbance was proposed. The method was based on an improved control structure, and integrated the excellences of robust control method and optimal control method. The achievement process was given by an example. Simulation results indicated that the method can effectively restrain disturbance, and reduce the sensitivity of the system. In addition, it was found that the system robustness and tracking performance is preferable.