Abstract: Topic of the paper was to correct the vignetting of mosaic images based on reflector. The generation mechanism of the vignetting phenomenon was analyzed through geometrical optics, and the vignetting energy distribution model in the middle of the optical field was proposed. According to the analysis result, a degenerate model which was calculated by the steepest descent method was proposed. The parameters of Hesse matrix were deduced to solve the problem of irregular quadrics fitting, then to correct the vignetting. The experiment result illuminates that the parameters of the degenerate model can be estimated effectively, the image's SNR after correction can be increased by 15 dB, and the vignetting can be removed effectively. The method can work in real-time working mode, and has extensive application value.