Abstract: By using upper air observational data, surface observational data, NCEP 1°×1°reanalysis data, 4 snow processes in Yunnan in winter 2013 were comparative analyzed and diagnosed.The similarities and differences were analyzed about formation mechanism of 4 snow processes, and so on.The results showed that in the 4 snow processes in Yunnan, snowing intensity and area caused by the south trough pattern was stronger than no south trough pattern on 500 h Pa obviously, the north higher and south lower about height fields, the front area density on 700 h Pa.Precipitation was obviously strengthened by the south west warm meets cold air. The strong water vapor flux convergence belt and area can better indicate the snow processes of Yunnan.The snow always appears in the area of strong water vapor convergence and closed to the side of strong cold air in the east and north of the convergence center. Because the updraft and the downdraft in the south and the north coexisted, the meso-scale vertical circulation near the front area may establish.When the cold air from the north moved to the south, the θ_sesharpness area also moved to the south, the coupling between the right entrance of the upper jet and the vertical circulation of the frontal zone, and then caused the water vapor brought by the south warm moist airflow to condense and the unstable energy to release, providing enough uplift condensation condition for the snow. Temperature condition was provided by moving to south about stronger ground cold high and involving about ground cold air, and were in favor of generating and supporting.