Heavy rainstorm appears at some stations, while doesn’t appear at the other stations in the precipitation cloud area of typhoon in practice, that bring difficulty to single station forecast. In this paper, in order to improve the accuracy of single station rainstorm forecast in this area, the means of multi-physical parameter synthesis diagnostic analysis is used to analyze the origin of vapor and the maintenance of instability stratification and secondary mid-scale convergence about multi-station typhoon “Rananim” to west, meanwhile, it discusses the occurrence and development mechanism of heavy rainstorm at single station and the reason why it doesn’t occur. The result shows that, the main reason that heavy rainstorm occurs at single station is the appearance of sub-circulation, such as ∑θse(5+7+8)≥230 ℃ at high latitude over station. It takes on obviously negative thermal advection at 200hPa over station, but positive thermal advection at 850hPa over station. The high and low level of the station are both positive vorticity center, and the value at low level is more than the value at high level. Divergence takes on negative center at each level;or it takes on positive center at high level and negative center at low level. The center value of vertical velocity should be less than 140 10-3 hPa／s at station. Incessant and enough vapor is needed at the station, and vapor convergence is also necessary. The strong water vapor transports over northwest of typhoon center is close with the maximal gradient of dry tongue over typhoon west center ,and also lies near to the maximal convergence of wind direction and wind speed.When the factors above appear entirely at station of precipitation cloud area of typhoon, heavy rainstorm is easy to occur.