For a meniscus mirror with 620 mm diameter and 18 mm thickness, active correction of surface-profile error is carried out. Through flotation support, the spatial position of the mirror is fixed. The support system of the mirror consists of 36 axial active supports and 6 lateral passive supports. Three points in the middle circle of axial supports are chosen symmetrically as dummy hard points, and the flotation support is achieved through adjusting the support forces of other actuators to null the dummy hard point forces at all times. The Hartmann wavefront sensor is used as testing equipment and the least square method is used to calculate the active corrective forces. In the experiment, the correction ability of the active supports is analyzed first and low-frequency Zernike terms are selected for correction finally. Then the close-loop and open-loop correction at different elevations is carried out, and the results show that through flotation support, the surface-profile error can be corrected effectively without piston and tilt. More than 0.6λ (λ=632.8 nm) root-mean-square (RMS) of surface-profile error of the initial state can be corrected to λ/15 at any elevation angles, and the RMS of correction precision of open-loop reaches λ/10～λ/14. Through the experiment the feasibility of correction process with varying elevation angle and the arithmetic of correction forces are discussed, and the control of mirror position through flotation support is approved.