A heavy rainstorm occurring in the northeastern border of the Qinghai-Tibet plateau on August 7 to 8, 2010 was simulated by using WRF numerical model. Based on the conventional observation data, FY satellite images and the model output, the macro and micro evolution characteristics and mechanism of the rainstorm were studied in more detail. The simulation of Milbrandt-Yau scheme with complete double parameters calculation process, would describe the cloud physical processes in detail. The description and treatment of cloud microphysical structure is complicated.The results indicated that the heavy rainstorm happened under favorable condition of South Asian high connecting with subtropical high, the divided shortwave trough in middle-high latitudes moving southward and meeting with southeastern warm air, which formed low vortex with shear line; a large amount of water vapor and unstable energy, low-level convergence high-level divergence of empty configuration provides necessary conditions for development of storm rainfall. WRF model has simulated this heavy rainstorm event quite well, such as precipitation area, centers, magnitude and scope of cloud merging process, as well as strong convective cloud. The cloud structure of precipitation is cold cloud precipitation. The graupel has the strongest ability to freeze the cold cloud water, and content of graupel is much larger than the ice and snow. The graupel melting is the main source of rain. There is few snow in clouds, which may be related to its cold weather caused by freezing cold water.