Abstract: Analysis of monthly and daily meteorological data, the national benchmark station precipitation data and outgoing longwave radiation using NCEP/NCAR（OLR, outgoing longwave radiation）, the climate diagnosis method, mainly from the aspects of circulation features, the West Pacific subtropical high and the East Asian Winter Monsoon characteristics, cold air and humidity conditions, analyze the causes of the preliminary diagnosis 2011 to 2012 winter drought in southwest China. The results show that the Siberia high pressure is obviously stronger than that of the same period of the year, and the strong feature of the East Asian Winter Monsoon makes the cold air position more northerly and easterly, and the cold air which influences the southwest and northwest is weaker than that of the whole year. It is not conducive to precipitation in Southwest China in winter. At the same time, the Western Pacific subtropical high was stronger than normal, the location of the North ridge line, is not conducive to the delivery of warm air to the bay of Bengal to the Yunnan Guizhou Plateau; in addition, Bangladesh Yunnan province area to show high OLR, inhibited due to convection, the weather continued fine little rain.

Key words: Southwest China, drought, atmospheric circulation anomaly, temporal and spatial distribution characteristics, dynamic cause of formation