In the development of the laser communication ground optical terminal, the dynamic stability of secondary mirror structure system plays an important role in ensuring the high image quality and stable optical axis orientation. By means of Finite Element Method (FEM), the dynamic stability of secondary mirror structure system has been analyzed by applying variable offset distances and preloads. The natural frequency of secondary mirror structure system increases with the offset distances, presenting a maximum around 20mm at variable preloads. While, the curvilinear relationship between natural frequency and preloads shows a monotonic increasing function. The results provide a theoretical reference to improve the torsional stiffness and the dynamic stability of secondary mirror structure system, which helps to optimize the structure design of secondary mirror system of laser communication ground optical terminal.