The relationship between Yunan rainy season early or late onset and South Asia high variation at 100hPa,geopotentical height anomaly feature over mid-high latitude at 500hPa was analysed.It is concluded that characteristic law of El Nino/La Nino events and southwest monsoon onset,Yunnan rainy season early or late onset was presented.The forecast thinking of Yunnan rainy season early or late onset was suggested.