An active optical experiment was carried out by a mirror with a diameter of 400 mm and a thickness of 12 mm. The support construction of the mirror included 12 active supports and 3 fixed supports,in which the active support was implemented by force actuators consisting of piezoelectric ceramic actuators and loadcells. The active supports were used for controlling the surface of the mirror,and the fixed points were used for positioning the mirror. In the experiment,the mirror surface was tested by a Zygo interferometer. The surface error of the mirror was tested before and after an actuator exerted a unit force on it lonely,then the difference between the two surface errors was calculated to be as the response function of the actuator,and the response functions of all the actuators made up a stiffness matrix. Afterwards,the damp least square method is used to determine the active corrective force and the process of exerting force of the actuator was controlled by a PID arithmetic. The experimental results show that the surface error is corrected from 1.22λRMS to 0.12λRMS,which is close to 0.1λ that is the surface quality after polishing. The experiment shows the active correct arithmetic and procedure is correct and feasible.