Abstract: The climatic characteristics, circulation patterns and physical field features are analyzed,based on the daily weather phenomenon data (1981—2013) of 124 stations of Yunnan Province and NCEP/NCAR(2.5°×2.5°) re-analytical data.The results show: Firstly,in over 30 years (1981—2013),the snowfall showed an obvious declining trend in Yunnan.The declining rate was 0.6 time every 10 years,which passed 95% of significant tests.The snow fall in Kunming mainly appeared in December and January,with the earliest in November,and the latest in March.The continual snowfall mostly lasted 2 to 3 days,the longest lasting 5 days,and the shortest,just 1 day.Secondly,the snowfall processes in Yunnan are affected by the weather systems of the high latitudes as well as the low latitudes and they are also influenced by the ground and near-surface weather systems.Seen from the 500 hPa circulation system,the north-ridge-and-south-trough pattern is the most important that causes rainfall and snowfall in winter and spring in Yunnan Province.The south branch trough is one of the important weather systems leading to the large-scale rain and snow in Yunnan.The shear line weather system of near-surface is also important in causing the large-scale rain and snow in winter and spring in Yunnan.It is the southward influence of the cold air that leads to the large-scale disasters of rain and snow in Yunnan Province.Thirdly,Yunnan's snowfall processes are mainly divided into three categories: the pattern of the north ridge and south trough,of the north transversal trough with south trough,and of the north transversal trough without south trough.Fourthly,there are some similarities and differences between the three snowfall patterns in water vapor transmission,and thermal and dynamic conditions.All three snowfall patterns carry abundant water vapor to Yunnan from the west and south and provide favorable vapor conditions for snowfall.The difference is that the water vapor of snowfall processes with the south branch trough comes from the Bay of Bengal,while that without the south branch trough comes from the Arabian Sea.The three snowfall patterns in Yunnan are under the thermal conditions of high temperature and humidity,which can produce heavy snow (rain) because of the uplift of cold air invasion.The intensity of cold air is greater in the transversal trough pattern than in the north ridge pattern,and the cold air influencing Yunnan is southerly and westerly.The intensity and position of ascending motion of the three snowfall patterns are different,which determines the size of areas and the intensity of the heavy snow (rain).