In order to reduce the thermal-deformation of the silicon mirror, a finite element method analysis system about the thermal-deformation of the mirror is established. The thermal-deformation of the mirror with different semiconductor refrigeration powers are compared, then, for the TEM00 mode Gaussian beam whose radius is 1/3 of the mirror, the structure of the mirror is optimized when the absorbed power is 50 W. The optimized mirror in the TEM00 mode Gaussian beam of different parameters and TEM10, TEM11 mode Hermite-Gaussian beam under the irradiation of the thermal deformation are analyzed. The simulation results show that when the semiconductor refrigeration power equals the power of the laser absorbed and lags behind the laser works, the deformation is largely improved and is relatively stable at last. In addition, when a circular area with thickness of 1.4 mm and inner radius of 25 mm is removed at the backside of the mirror, the peak valley (PV) value is 0.005 mm. The PV value of the thermal distortion of the optimized mirror is reduced in a certain extent under other laser radiations. For TEM00 mode Gaussian beam and TEM10, TEM11 mode Hermite-Gaussian beam, the mirror satisfies the requirement of the optic system.