Heavy rain event on September 11 2002 in Lingshi and Heshun, Jinzhong city, Shanxi province is diagnosed. The results show that the event is caused by active subtropical high, at the moment, there is also a uncertain cold front on the surface. The area where the heavy rain event lies to center of high energetic humid tongue. Low-layer humid tongue lags behind mid-layer humid tongue. In addition, local meteorological factors and local topography could be taken for factors of the reference to forecast local heavy rainfall.