In order to solve the impact of fast illumination change on moving object detection in a visual surveillance system, a new method of moving target detection is put forward. Through establishing illumination change model, the chromaticity difference model and brightness ratio model are used to eliminate the impact of fast illumination change. When fast illumination is changing fast, background pixels and moving object pixels are detected as foreground pixels. To separate moving object pixels and false foreground pixels from detected foreground pixels, chromaticity difference model and brightness ratio model are developed respectively to estimate the intensity difference and intensity ratio of false foreground pixels. The establishment of Chromaticity Difference Model (CDM) and Brightness Ratio Model (BRM) are based on the proposed illumination change model. The experimental results show that the method has good detection effect and real-time in the rapidly changing of illumination conditions.