An integrated simulation method is established, and the performance assessment of optical systems is obtained, accordingly. New assessment functions are used for rigid-body displacement separation, which is conducted by deformation data from the Ansys thermal simulation. The computational accuracy of 0.3% is tested through setting displacement parameter and random value. Householder algorithm is adopted for Zernike fitting, and the Zernike coefficients are used as the interface for data exchange with Zemax, which is achieved by dynamic data exchange technology. The simulation of an objective lens is taken as an example, and a distortion-thermal curve is presented. The result indicates that in order to guarantee measuring accuracy of 1″, the working temperature should be in the range from 14 ℃ to 26 ℃.