Performances of a 20-element bimorph deformable mirror are measured and a closed-loop adaptive optics system, which consists of the bimorph mirror and a Shack-Hartmann wave-front sensor with 13 x 13 sub-aperture array, is established to test the mirror's capability of correcting static aberrations. Experimental results show that, the mean displacement response to voltage of discrete actuators is 0.57 mu m/100 V and that of defocus electrode is 1.09 mu m/100 V. The hysteresis of actuator is limited to ten percents of the maximal displacement. With the ambient temperature increasing from 13 degrees C to 25 degrees C, the P-V of defocus of the mirror surface is enlarged by 1.37 mu m and the P-V of other distortions, such as astigmatism, coma and spherical aberration, is enlarged by 0.15 mu m. The frequency response of the bimorph mirror is about 4 kHz. When the closed-loop control is on, intensity distributions at the image plane of distorted wave-fronts are effectively improved. The Strehl ratios increase from 0.02 to 0.95, and 0.03 to 0.54, respectively.