As Electric-Optic(EO) stabilized platform is effected by the disturbance of friction, windage, unbalance and base motion in stabilizing a Line of Sight(LOS), this paper explores the mechanism and method to eliminate the disturbance torque by a high order observer. The observer is consist of an inverse system of the control object and a modified filter, and the modified filter is implemented by a high order design. The observer is used for observing the disturbance torque, then the current loop with a very high bandwidth is utilized to compensate the disturbance torque. The eliminating disturbance ability of the system is simulated.The results show that the high-order disturbance observer has the ability to eliminate the high-order disturbance model: the 3th order observer eliminates the disturbance by 100% for the step and ramp disturbance; and eliminates the disturbance by 99.9999996% for the parabola disturbance. Moreover, the observer also has good robustness to the perturbation of the control object. The method improves the response speed of the servo system meanwhile ensuring the robustness of the system, so that it satisfies the application requirements of the EO stabilized platform.