An observer-based active disturbance rejection control (ADRC) method is proposed to improve the response speed and anti-interference ability of photoelectric theodolite in tracking. All the known or unknown disturbances affecting the operation of the DC motor are estimated online, and these disturbances are compensated by appropriate feedback control methods. By selecting the appropriate observer and controller bandwidth parameters, a good anti-disturbance control effect is achieved. The simulation results show that the observer-based active disturbance rejection control method can effectively improve the robustness of the DC motor against external disturbances and internal unknown parameter changes, and has engineering application prospects.