Using conventional observation and 10°×10° NCEP re-analysis data for 3 regional heavy rain storms in summer of 2008, the interaction mechanisms of low-level jet, water vapor field and energy front, which cause the rainstorm, is discussed in this paper, based on the synoptic analysis. The results show that low-level jet plays an important role for the delivery of vapor moisture and energy. On one hand, low-level jet provides much needed vapor moisture for the creation of rainstorm, on the other hand, it makes the lower atmosphere of rainfall area warming and humidifying, causing the convective instability to strengthen and vertical ascending motion to be severe, supplying a large amount of unstable energy for the occurrence of rainstorm. Low level jet, the wide and thick zonal cross-section of wet-column as well as the location, intensity of the energy front correlate closely with the level and the falling area of the heavy precipitation.