Abstract: In order to solve the optical axis deflection owing to asymmetric thermal deformation of mirror induced by irregular facula, phase change cooled mirror, which takes the place of normal silicon mirror, is presented to minimize PV value of deformation on mirror surface and mirror deflection. Online tests are carried out on 2kW CW carbon dioxide laser. The experimental results indicate that: Compared with normal silicon mirror, phase change cooled mirror achieves more uniform temperature field on surface. It can diminish angle of mirror deflection and centroid drift, and improve the beam quality in the far field.