For an in-deep analysis of temporal and spatial changing characteristics of ET_0 in the five provinces of Southwest China(Guangxi Zhuang Autonomous Region, Chongqing Municipality, Yunnan Province, Guizhou Province, Sichuan Province), daily climatic data in 119 meteorological stations were used to calculate ET_0 using Penman-Monteith(P-M)equation by FAO. In addition, Mann Kendall rank correlation, Morlet wavelet method and interpolation of GIS were applied to a quantitative analysis of the spatial-temporal variations characteristics of ET_0. Results showed that the annual mean ET_0 of the five provinces of Southwest China was 855 mm, the fluctuation range was 819~901 mm over the past sixty years, and the ET_0 had a decreasing trend with a rate of 1.5 mm per decade for annual series. The descent speeds were -0.4 mm/10a, -0.7 mm/10a, -0.3 mm/10a, -0.1 mm/10a in spring, summer, autumn, winter, which accounted the annual decreasing trend for 26.7%,46.7%,20%, 6.6%. The annual ET_0 of the five provinces of Southwest China existed anincrease- decreasealternating change with periods of 26, 12 and 5 years. 26, 12 and 5 years were the first, second and third periods respectively; During the past 60 years, the the annual mean ET_0 in the south was greater than that in the north, those in western Yunnan-Guizhou plateau and the Guangxi area were significantly greater than those in the Sichuan basin and eastern Yunnan-Guizhou plateau. Sichuan basin was relatively minimal, those in the south of western Sichuan plateau and eastern Yunnan-Guizhou plateau area were the relatively largest; In spring, summer, autumn and winter, the higher values were found in western Yunnan-Guizhou plateau, Sichuan basin and eastern Yunnan- Guizhou plateau, Guangxi area, wastern Yunnan-Guizhou plateau, the lower values were found in Sichuan basin, western Yunnan-Guizhou plateau, Sichuan basin and the north- east of western Sichuan plateau, Sichuan basin and Guangxi area.