Abstract: The WRF (Weather Research and Forecasting) model was used to numerically simulate the heavy snowfall process that occurred on 30 November 2018, in the Ili River valley and the northern slope of the Tianshan mountains and to analyze the vertical velocity and vertical kinetic energy change mechanism of heavy snowfall under complex terrain. Studies have shown that the passage of a cold front increases the surface pressure and the dry air mass in the column, leading to changes in the vertical pressure gradient force and the dry air column buoyancy, which in turn causes the development of vertical motion. The local time variation of vertical velocity mainly depends on the perturbation vertical pressure gradient force, drag force of the water substance, and perturbation dry air buoyancy. When the airflow crosses the north slope of the Tianshan mountains, the perturbation vertical pressure gradient force on the windward slope becomes larger, and the perturbation dry air buoyancy becomes smaller, promoting the upward movement. On the leeward slope, the perturbation vertical pressure gradient force and the perturbation air buoyancy form a downward total force produce sinking acceleration, which results in a strong sinking gale of the leeward slope. The work done by the perturbation vertical pressure gradient force is basically contrary to the work done by the perturbation dry air buoyancy. On the leeward slope, the work items of the perturbation vertical air pressure gradient force and the comprehensive force are to suppress the vertical kinetic energy, while the work item of the perturbation dry air buoyancy and the drag force of the water substance enhances the vertical kinetic energy. In addition, the work items of the perturbation vertical pressure gradient force and the perturbation dry air buoyancy mainly appear in the middle and low layers, the work items of the water material drag force are mainly located in the lower layers, and the comprehensive force work in flat terrain is significantly less than that in complex terrain.