Based on the observational data and the mesoscale numerical model WRF, a typical low-vortex low-trough snowfall system that occurred in Beijing on 14 February 2019 is analyzed and numerically simulated. The microphysical mechanism and formation process of snowfall are discussed, and the numerical simulation of cloud seeding is analyzed. The results show that the water vapor caused by warm and humid advection near the low vortex front and the strong upward movement near the low vortex shear line gave rise to the regional snowfall event. The sublimation growth of snow, the cloud water rimming on falling snow, the automatic conversion of cloud ice into snow, the ice crystals and snow collisions and aggregation were the main microphysical processes. Seeding simulation shows that after the seeding of silver iodide (AgI), a large number of ice crystals are generated in the cloud, and the increased ice crystals are converted into snow through sublimation growth, collision, aggregation and attachment, etc., which in turn leads to an increase in ground snowfall.