Based on the synoptic analysis for a rainstorm event occurred in Chongqing on 29,30 May 2004,the nonhydrostatic version of mesoscale numerical model MM5 was used to simulate this case with two nested domains.The diagnostic analysis results show that the moving cold-front cloud system produced by a high-level trough is the main synoptic system of this rainstorm,and a meso-vortex produced by the trough is the main mesoscale system.The comparison between simulated and observed data shows that MM5 can successfully simulate the rainstorm event in the east of the Sichuan plain.It is pointed out that the meso-vortex convergence and the intense ascending movement produced by the east-moving trough in the Chongqing area engendered the rainstorm.