Compared with conventional stack actuator deformable mirrors, the bimorph deformable mirrors have more simple structures, larger stroke, lower cost and less time consumption. Therefore, they are potential substitutes of stack actuator deformable mirrors in adaptive optics systems. A prototype of 20-element bimorph deformable mirror is designed and fabricated in order to verify the process and investigate its basic characters. This prototype has two PZT layers, the outer one is divided into 19 electrodes, and the inner one has a whole defocus electrode. The influence functions of the fabricated prototype are measured by using a Veeco interferometer and the correction ability for the first 36 Zernike aberrations is simulated. The results show that it has a good fitting ability for low order Zernike aberrations, especially for defocus, and it achieves an amplitude more than 8 μm. And this ability decreases as the increase of space frequency, which indicates that this bimorph deformable mirror is very suitable for correcting low order aberrations. In addition, fitting abilities of the fabricated prototype for correcting Zernike aberrations with different clear apertures are discussed.