The structure of a typical photoelectric tracking system was analyzed and a method to improve the resonant frequency of mechanical structure was proposed to improve the tracking speed of the photoelectric tracking system. The structure of the vertical bearing of a typical tracking frame was researched， and it pointed out that the torsional stiffness of the system was limited by the movement of a one-way thrust bearing along axial direction. Then， a structure of double thrust bearing combined with centering bearing was proposed to design of the vertical axis. By which the system stiffness was enhanced and the resonant frequency of mechanical structure was improved. A modal simulation on the improved tracking gimbal was analyzed， the resonance frequency curve of photoelectric tracking system was obtained through the experiments of vibration and sweep frequency. The results show that the resonant frequency of the system is up to 114 Hz，which provides a hardware support for the stability and higher speed of servo system. In the actual task， the maximum tracking speed and the acceleration of the system is above 150 (°)/s and greater than 240 (°)/s2， respectively， improving the tracking ability of the photoelectric tracking system significantly.