Abstract: Based on the conventional meteorological data and reanalysis data from NCEP, the heavy snow process on January 6, 2001 was analyzed. The results show that the south warm and humid airflow climbing along the southward cold air cushion is favorable to snowfall. Backflow snowfall is the main in this snow, while snowfall from west trough is the main in the late of this snow. It will have the strong ascending motion and plenty of water vapor transport and convergence when the heavy snow happens. The development of high level divergence and low level convergence together with positive vorticity in the middle and low level could provide dynamic conditions for the heavy snow, especially the concentration of positive vorticity advection. The southerly jet could afford abundant water vapor and energy for snowfall. Convergence area of ageostrophic wet Q-vector is accorded with snowfall area. Evolvement of the low level high energy tongue could determine the time and position of strong precipitation approximately. Convective instability appears at the stage of backflow snowfall.