Abstract: In order to correct the defocus aberration in the thin-disk laser resonant cavity, a special water-cooled deformable mirror named as defocus-correction deformable mirror was designed and manufactured. The defocus-correction deformable mirror has 5 piezoelectric ceramic actuators, one located in the center of the round mirror surface and the other four arranged symmetrically on the mirrors circular periphery. The simulation of relationship between mirror thickness and surface deformation was carried out to gain the best defocus-correction result. Testing results show that, the deformable mirror, with optical surface quality better than 034 m PV, has extremely large stroke up to 16 m. In the wavefront correction experiments of thin-disk laser systems, the optical quality ( factor) of laser was improved from 19.5 to 6.5, which gives the vivid proof of the capability and effect of the defocus-correction deformable mirror.