The thermal distortion of the deformable mirror (DM) arised from the high-power continuous laser beam brings about the phase distortion and further degrades the beam quality. The model for the DM is built up using the finite element analysis software ANSYS. The characteristics of the thermal distortion of the DM and the reflective mirror are analyzed and compared. The influence of structural parameters of the DM on the incident light phase are also discussed. The results indicate that, the thermal distortion of the DM is more obvious compared with the high reflective mirror. The high frequency phase distortion introduced by thermal distortion increases with the decreasing of the spacing of heads. The length of heads exhibits a significant influence on the high frequency components and the high frequency phase distortion increases with the decreasing of the length of heads. As a result, high frequency phase distortion introduced by the thermal distortion can be diminished through increasing the length of heads appropriately. The proportion of the high frequency phase distortion decreases with the increasing of the diameter of heads, leading to the decreasing of correction capability. Consequently, the diameter of heads should be considered comprehensively in the practical application. The results obtained can provide valuable reference for the parameter optimization of the DM.