Abstract: Calculating the number of frozen days in January in southwestern China when satisfying the conditions with daily minimum temperature in the context of -10℃ and 1 ℃, relative humidity greater than 80%, and sunshine duration less than or equal to 2 hours at the same time, by using daily meteorological elements data for the period of 1961－2009 from 96 stations in southwestern China. Using NCEP/NCAR reanalysis grid data, the circulation features in the icing and no-icing years were analyzed. The results show that, in icing years in southwestern China, the 500-hPa height anomaly field are “north-higher and south-lower” in Eurasia, “west-higher and east-lower” in the high latitudes, and “west-lower and east-higher” in the low latitudes, indicating that the high pressure around the Ural Mountains, depression around the Caspian Sea, and the subtropical high are all strong, in favour of cold and warm air confluence in southwestern China, which is the basic condition of icing there; the best related areas of the Middle East jet stream and the icing in southwestern China are the boundary of Sichuan－Yunnan－Guizhou provinces, most of Guizhou Province, the boundary between northern Yunnan Province and southeastern Tibet, the southwest of Shaanxi Province, and about Erlang Mountain, which are the most areas of strong icing on average. Further studies indicate that 500-hPa trough activity around Central Asia is the bond between the Middle East jet stream and the icing in southwestern China. If the sea surface temperature near Bermuda in the north Atlantic is colder in the prior December, the Middle East jet stream will be much stronger in January.