This study simulated a warm-sector rainstorm event that occurred in Yongji, Jilin province on July 13 2017, which reproduced the development process that include the initiation of convective cells and linear system, organized and the stagesthat form bow echo; based on these data, the cloud microphysical characteristics of the mesoscale convective systems were analyzed, and then discussed the possible cloud microphysical mechanisms causing the warm-sector precipitation. The simulated results show that this precipitation process in the Yongji occurred in a favorable multi-scale environmental configuration dominated by the northeast cold vortex. The mesoscale systems was mainly the cold cloud systems. The warm zone had a large range, so that the location of supercooled water was high, and ice and supercooled water coexisted, the "seeding" effect of the coexisting area caused a large amount of graupel. Diagnoses of the mass- and heat-hydrometeor budgets showed that the main source of rainwater was the accretion growth of cloud droplets, and the main sink was the collection of raindrop by ice during the triggering and organization of the precipitation system; while in the bow-shaped echo stage, the melting of graupel add to the main source terms, the main sink terms were the evaporation of rainwater in the lower layer and the collection of rainwater by the graupel in the upper layer. The main heat source of warm-sector precipitation was the latent heat release from condensation of water vapor, and the main cooling term was the evaporation of rain and cloud water. In the bow-shaped echo stage, confluence of the inflow at the front and the backward inflow above the cold pad on the ground bring water vapor into the upper layer, and the "seeding" effect significantly increased the content of the graupel particles near the height of 8km from the ground, which coincided with the high temperature area formed by the condensation of water vapor to release a large amount of latent heat. Therefore, a large amount of graupel melted into rainwater, resulting in a strong precipitation process.