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利用1980-2008年近30年逐日地面、高空观测资料，统计了影响云南的西风带南支槽个例，并分析了南支槽的时空分布和对云南降水的影响。结果表明，影响云南的南支槽平均每年出现18．76次，11月-次年5月平均每月出现次数相当（6-10月西风带北撤，转换为孟加拉湾槽）；约5．88％的南支槽过程对云南产生大到暴雨天气，54．83％的南支槽产生小到中雨，另有17．28％的南支槽产生冰雹天气过程。南支槽的进退与西风带环流形势、副热带高压位置和高原大地形等关系密切，南支槽位置、水汽输送、湿度锋区、低空急流和冷空气强弱等条件的不同决定了降水的强弱或是否有强对流天气出现。“,”Using the daily surface observation and radiosonde data from 1980 to 2008, the cases of the south branch trough of westerlies influencing on the weather of Yunnan Province are investigated. The spatial and temporal distributions of the south branch trough of westerlies and characteristic of influencing on the precipitation of Yunnan are analyzed. The results indicate that the yearly averaged number oc curred south branch trough of westerlies influencing on the weather of Yunnan is 18. 76. The monthly mean numbers from November to May in next year are almost the same. About 5. 880//00 of processes of the south branch trough will produce the weather from heavy rain to rainstorm in Yunnan, about 54.83~ of processes will produce the weather from light rain to moderate rain in Yunnan. Other 17.28~//00 of processes will produce the hail weather. The result shows that the advance and retreat of south branch trough are closely related to the westerly belt circulation, position of subtropical high, the large-orography of plat- eau, and so on. The intensity of precipitation and occurring of severe convective weather in Yunnan are de- termined by the position of the south branch trough, water vapour transporting, moisture from zone and low-level jet and strong and weak cold air, and so on.