laser tracker is composed of a mechanical structure and a servo control system. and the characteristics of them all affect the error and stability of the laser tracker measurement system. the cut-off frequency and the response speed are important index to characterize the system performance. among them, the cut-off frequency is the characterization of the size of the system bandwidth, and response speed is an indicator of system sensitivity. the cut-off frequency is higher, and the response speed is faster. the tracking performance of the tracker is better. usually, when analyze the cut-off frequency of a system, various components of the control system will be the mathematical modeling, but only the mechanical structure of the inertia as a parameter into the model. it can cause errors in system analysis. in this paper, establish a mechanical and electrical model of the mechanical structure and the control structure to realize the information of the laser tracker system. analyze the effects of rotating inertia, friction torque and structural rigidity on the characteristics of electromechanical coupling system.