After detailed analysis of summer heavy rainfall in Jinzhong, Shanxi Province from 1974 to 2000, it is pointed out that the northwest vortex (34-37°N, 95-103°E), and the southwest vortex (28-34°N, 93-97 °E) over 700hPa are the most original trigger mechanism of summer heavy rainfall in Jinzhong city. The vortexes, the high-and low-layer synoptic patterns, the vapor passage and the position of wind shear line could be taken for the factors to forecast heavy rainfall in this area.