The WRF (Advanced Weather Research and Forecasting modeling system) was employed to simulate the local severe rainstorm process caused by typhoon Haikui over the northwestern of Zhejiang Province from 6 to 9 August 2012. The analysis of the simulation result combined with Doppler radar data, TBB (Temperature of Black Body) data, and automatic weather station data shows that there are several mesoscale systems embedded in spiral cloud band of the landed typhoon. Mesoscale systems develop, reinforce and weaken after division from spiral cloud band. It brings the local severe rainstorms over the northwestern of Zhejiang Province due to the direct effect of mesoscale systems. There generates the mesoscale divergence line which is responsible for the rainstorm by northeasterly flow and northwesterly current under advantageous topography. The topography of the northwestern of Zhejiang Province can increase the intensity of rainfall but is not so related to typhoon track and range of rainfall.