Thermal deformation and stress have an important influence on performance of ring laser gyroscopes (RLG) in high-low temperature. The traditional design methods of RLG are focus on optical performance of resonator more than mechanical and thermal performance. Generally, the traditional structural design of resonator is dependent on experienced equation and experiment, which result in more iterative design and lower efficiency. Relationship between thermal performance and structural parameters is studied by finite element (FE) method in resonator of mechanically dithered ring laser gyroscopes, the temperature field of resonator and relationship between thermal performance and structural parameters are obtained, which provide the resonator of mechanically dithered ring laser gyroscopes with significant and directive method. It has significance to improve efficiency, shorten hour and reduce cost.