Based on some routine sounding data, surface meteorological observation, automatic meteorological station and hydrological data, T213 numerical forecast and satellite pictures, the synthesis analysis of a heavy rainfall occurred on longhui is made. The results show that: the heavy rainfall happened on the condition of two-trough and one-ridge current pattern in the mid and high latitude of Eurasian .The trough line and shear line are the main influential system; the important conditions causing the event are the strong instability of atmospheric stratification and severe vertical motion. The vapor at 700hPa comes from the Bay of Bengal and South China Sea, and vapor at 850hPa 500hPa is from South China Sea. There are strong energy transportation and accumulation in the low levels before the rainfall, as well as the atmosphere motion is changed from descending motion to ascending motion in the whole rainfall area. The Q vector convergence at low levels is correlated well to the downfall area and time. The low-level positive vorticity, the high-level negative vorticity are in agreement well with and low–level convergence and high-level divergence. The effects of pumping and feedback strengthening lower convergence, reinforce the development of heavy rain, form very favorable .are very favorable for the heavy rainfall.