The thermal-structural-optical integrated analysis method has been widely used to evaluate the impact of environmental load on performances of opto-mechanical systems. However, for opto-mechanical systems with complex optical surface deformation mode and large rigid body motion, the results obtained by the traditional thermal-structural-optical integrated analysis method are inaccurate. A modified thermal-structural-optical integrated analysis method based on the complete equations of rigid body motion was proposed. Firstly, the deformed optical mirror was modified by bicubic spline interpolation method, then the complete equations of rigid body motion of the optical surface was established. The rigid body motion of the optical mirror was separated by a common optimization algorithm, and finally Zernike polynomial coefficients were solved by the least square method to characterize the elastic deformation of the optical mirror. Numerical and engineering cases were used to verify the effectiveness and correctness of the proposed method. The effects of key factors such as rigid body motion equation, surface correction method, node distribution and surface shape on the results were also quantitatively analyzed. The results show that the proposed method can identify the rigid body motion and elastic deformation of the optical surface more accurately than the traditional method, and does not depend on the analytical equation of the optical surface, and the shape of the mirror surface has a great influence on the analysis results.