Based on the conventional observation data and NCEP 1 °× 1 ° reanalysis data, three typical cases of regional blizzard, heavy snow and moderate snow in Jiangsu Province are compared and analyzed. It is found that the location and intensity of 700hPa low-level jet is one of the main factors affecting the magnitude of snowfall, and the vertical distribution of the vorticity over the snowfall area follows the low-level negative vorticity and medium level The configuration of positive vorticity and negative vorticity in the upper layer shows that during blizzard, the positive vorticity is strong and the positive vorticity area is the deepest, and the dynamic uplift is strong, while the positive vorticity area is relatively shallow when the middle snow occurs, which is not conducive to the formation of strong convergence and uplift, and the dynamic uplift is weak. In addition, when Blizzard and Blizzard occur, the whole layer is basically positive area of vertical helicity, and there is no obvious positive area in moderate snow; in the process of Blizzard and blizzard, there is an obvious inversion layer in the middle and low layers, and the explosive increase of temperature in the middle troposphere caused by southwest jet in the middle and high layers is the key to the formation of inversion layer, and there is not necessarily inversion layer knot in the occurrence of moderate snow; the intensity of snowfall and the component of moist potential vorticity are absolute There is a positive correlation between the values.