Abstract: During the process of optical design and assembly，it is necessary to estimate the performance of optical system based on the surface quality of the mirrors. The traditional way is to use the Zernike polynomial, which is restricted to depict the consecutive and smooth surface. Otherwise, get the ideal surface during aspherical surface polishing is very difficult, the mid-and-high frequency errors which is very harmful to the optical system's image quality will be produced at the same time. In this paper, a new point-to-point method was introduced, any surface with mid-and-high frequency errors could be exactly simulated, and the optical system's performance can be estimated accurately. An example of the optical system was cited, it was revealed that the camera's simulated performace is very close to the measurement, the coincident to real system is over 90%.