Abstract: It has been demonstrated that methods of clamping for laser mirrors affect thermal deformation greatly. The characteristics of several clamping methods are analyzed and the corresponding thermal deformation and largest stress of silicon mirror are calculated. It is concluded that the clamping method with buckling ring has an advantage over the pressing method with clamp plate in PV value of deformation on mirror surface. Moreover, the stress fractures for mirrors with these methods of clamping are analyzed.