Abstract: A heavy rainstorm during 17th ~ 18th August, 2012 in Sichuan Province was simulated by WRF model. Diagnoses were made bases on the output data to get the influence of complex topography.Results show that, the WRF model successfully revealed the circulation and the rainfall. The water vapor comes from typhoon-low itself carrying moisture and the outside of subtropical high. The development stage of cloud in central Sichuan corresponds more than one stations appear strong precipitation, the convective cloud cluster development is an important factor in triggering the precipitation. The environmental conditions of high temperature and humidity in the lower troposphere provided a favorable thermodynamic condition for the forming and developing of convective cloud cluster. The topography sensitivity experiment shows, cliffy topography height is proportional to rainfall intensity, by influencing the cliffy topography surrounding the physical quantity field distribution and influence of rainstorm precipitation intensity; the effect on the intensity of precipitation of relative humidity is less than the temperature.