An effective aperture of 120 mm continuous face-sheet, discrete actuator deformable mirror (DM) is designed and experimentally tested. DM is aimed to correct defocus, astigmatism and coma, and the parameters of the DM are optimized, and it has nine actuated points and three fixed points. The fixed points are used to determine spatial position of the mirror and the actuated points are used to generate desired surface. Actuators are linear step motors with springs on the pushing end, which convert displacement to force. Test instrument used for DM is 4D dynamic interferometer. The test results show that the DM can generate defocus, astigmatism and coma with high accuracy, and it has a large dynamic correcting range.