In this paper,MM5V3 model was used to simulate typhoon 0519 “LONGWANG”,and moist potential vorticity (MPV) evolution was derived from output of the model.we studied the mechanism of the storm rainfall deduced by typhoon from the view point of MPV.Results showed that slantwise vorticity development(SVD) is an important mechanism of the rainstorm in Fujian coastland.The heavy rain occurred in the stiff and dense section of θse and isoline of MPV1 dense region in mid-low level of troposphere,minus area of MPV2 could be regarded as the trace of warm-moist airflow or vortex motion,so MPV had strong indicative ability on forecasting of where rainstorm took place.In addition,the confluence of southward low-tropospheric cold air pervading from high latitude and southeastern warm-moist air of typhoon in Fujian coastland made the slope of θse isoline larger and cyclonic vorticity exquisite development,which had great effect on occurrence of storm rainfall.