Based on the differences of their synoptic situation, physical elements field, etc. two typhoon processes which affect South China 2—8 July, 2001, as an example, are discussed. The results show that the main reasons of differences from strength to falling areas of heavy rainfall in the two processes are follows: typhoon Durian interacted with westerly system in mid latitude, at the same time, moisture flux convergence dilated above 500hPa. On the contrary, typhoon Utor turns weakening after landing and it is only a isolated tropical weather system because of the obstruction of subtropical high pressure, and moisture flux convergence is located below 850hPa. Moreover, the wet potential vorticity(MPV) has better relation with heavy rainfall.