The Hartmann wavefront sensor is commonly used in adaptive optical (AO) system to measure the wavefront aberration. Noise and assembly errors decrease the accuracy of a Hartmann wavefront sensor, thus degrade the quality of the AO system. The moment theory, which has its origin in digital graphic discipline, is introduced into AO system. The Zernike moment is utilized as pre-processing filter because it is insensitive to noise and rotationally invariant. Hence the AO system becomes less sensitive to noise, and no high assembly precision is required.