This paper discusses a method used in the testing of the optical system and optical reflection mirror. This method was based on the interference. The interferential pattern was expressed by the series of the Zernike circle polynomials. The coefficient of the series was obtained by Gram-Schmidt normalization method and the least square method. This paper also discusses the method for removing the adjust error and the error of the testing system itself. The wavefront error and OTF was obtained from the series of the Zernike circle polynomials.