Abstract: According to the requirement of system, the incipient structure of the off-axis optical system without freeform surface was computed. Choosing the Zernike polynomials surface as freeform surface, using the relationship of aberration and the Zernike polynomials, the aberration of surface parameters correction system was adjust, and the system was optimized by using CODE V. The different examples of direct optimization method and step-by-step optimization method were compared, and result shows the step by step optimization method is more suitable for the system design. Simulation results show that in the entire field of view, the diameter root mean square(RMS) of spot diagram dispersion circle is less than 27 m, MTF value at 30 lp/mm is more than 0.197 and the maximum grid distortion is -7.15%.