Based on the two-axis semi-strapdown stabilized platform, how to realize the functions of disturbance rejecting and stable tracking was researched. Analysis was made to the stabilized platform and the model was established. The reason for selecting Auto-Disturbance Rejection Control (ADRC) method was analyzed by comprehensively considering the factors of control requirements, controlled object characteristics and control technical state, and the advantages of ADRC were given. The controller was designed with four modules as tracking differentiator, extended state observer, nonlinear state error feedback control law, and disturbance estimation and compensation. The result of parameter adjusting was also presented. Simulation verified the effectiveness of the controller designed by comparing it with traditional PID. Step response verified the effect of disturbance rejection. Through inputting sine signal, the effect of stable tracking was tested. The method of Monte Carlo verified the robustness of the control system when the model parameters of controlled object fluctuated around the reference value by 20%. Simulation results show that: 1) The effect of disturbance rejection is obviously better than that of the traditional PID;and 2) The tracking error of this controller is only 50% of the PID, while the robustness doubled.