Active optics experiment was carried out with a 400 mm diameter, 12 mm thickness mirror. The support system of the mirror includes 12 active support points and 3 fixed support points. The active support was implemented by force actuator, which was composed of piezoelectric ceramics actuator and loadcell. The active support points were used for controlling the surface of the test mirror, and the fixed points were used for positioning the mirror. The mirror surface was tested by Shack- Hartmann wavefront sensor, the active corrective force was calculated through damp least square method, and the process of exerting force of the actuator was controlled by PID algorithm. The initial surface error is 1.16λ (λ =632.8 nm) RMS. After active correction, the surface error is 0.07λ RMS，which is better than 0.1λ of surface quality after polishing.