The microphysical characteristics of Warm Conveyor Belt (WCB) within a Winter mesoscale snowstorm in southern Hebei were analyzed using aircraft observation data. Affected by the WCB associated with the Southwest Vortex Warm Front, the cloud can be divided into three layers in the early period of snowfall. There were a few small-size ice crystals in the upper part of the cloud. The thickness of the middle layer is equivalent to the thickness of the WCB (0.9km), in which the maximum liquid water content was 0.51g.m-3, with low concentration of ice crystals, and the vertical profile of liquid water content and adiabatic water content was similar. In the lower part of the cloud, the number concentration of ice crystal increased by two orders of magnitude, and the particle spectrum width increased significantly. The ice crystal habits were predominantly of column, bundle of column and graupel. Graupel particals were formed through the process of riming that occurred in the middle layer with abundant supercooled water, and a large number of columnar ice crystals were produced by the Hallett-Mossop mechanism. The abundance of supercooled water in the WCB had an extremely important influence on the microphysical processes during the early snowfall period. The vertical structure of the cloud was relatively uniform in the later period of snowfall, due to the jet at 700hPa had moved out of the observation area. At this time, the ice crystal habits were predominantly of plate, and the particle size increased as the height decreases, reflecting the growth of the ice crystal through aggregation process.