A heavy rainstorm occurred over north Ningxia on July 29th 2012. In this paper, this heavy rainstorm event was analyzed by using the upper-air observation data, ground automatic weather station data and products of WRF model. The result shows: this heavy rainstorm occurred at the backdrop of beneficial large-scale circulation; and topography of Helan Mountain caused the lower wind convergence and detonated the heavy rainfall; the main influencing weather systems are southerly warm-wet air at 700hPa, shear line at 850hPa and meso-β shear line at ground; These weather systems stored and detonated unstable energy, and provided plentiful vapor and dynamic for the occurrence and maintain of short-term heavy rainfall. The results of numerical simulation show the HeLan Mountain terrain have obvious positive contribution to the formation of a Heavy Rainstorm over Yinchuan Plain.