Abstract: In order to more deeply study the impact of topography to the heavy rain, improve the rainstorm forecast accuracy, the author used the NCEP data and WRF model, the numerical simulations and analysis were conducted for a heavy rainstorm event occurred on July 21 2012 in Beijing, Hebei. The results showed that: the heavy rainfall was in favorable environment and special terrain occurred under the action of this area. Heavy rain center main valley, the mountains and plains of border area, was closely related to the effects of topography. Two aspects of terrain effects mainly thermodynamic and dynamic: wind valley while blowing, obvious form of high temperature, high humidity and water vapor transport, ascending motion, formation of convergence; mountains and plains along the border between the temperature gradient in the windward slope, plus the role, was conducive to the development of convection.