Based on PSU/NCAR′s mesoscale model MM5(V3.7), the typhoon Aili rainstorm event is investigated. The results show that the anisomerous distribution of wind field is one of reasons causing Typhoon turning. The center of rainstorm is in the high value area of Convective Available Potentional Energy (CAPE), the center of Storm Relative Helicity(SRH), and the common boundary of positive and negative Qvecter divergence. The sensitive numerical experiments are also conducted. It is concluded that terrain have significant impacts on vertical motion, intensity and distribution of heavy rainfall