Abstract: The heavy rainfall caused by typhoon 8209 is studied with the PSU/NCAR MM4 model.For control case,the ECMWF analysis is taken as the initial field, while the GMS satellite data are used to modify the initial moisture field for comparison. The results show that the simulated position and amount of rainfall maximum are better in case of using satellite data than that of control case. In addition, the assymmetric flow in typhoon are analysed and shown to be clcoely related to rainfall maximum. The mesoscale structures of this typhoon are analysed and the results show that there is a cyclonic vortex in low troposphere and there is anticyclonic circulation in upper troposphere for area of maximtum rainfall.