In order to study the thermal characteristic of fast steering mirror during the working process of high power CW laser, a time-dependent fast steering mirror model coupled with heat transfer and structure mechanic was established to calculate the distribution of temperature, thermal deformation and thermal stress by finite element software, and the material was fused silica, zerodur and sic respectively. The wave front of fast steering mirror was fitted by Zernike polynomial algorithms. The results indicate that under the same laser power irradiation conditions, the minimum temperature rising and thermal distortion of the three material is zerodur. By comparison, zerodur material is optimized as fast steering mirror, and its dominant thermal aberration are piston, spherical aberration and defocus, which can provide wavefront correction to theoretical reference in the field of engineering application.