Abstract: Yunnan is situated in a key position from tropical margin of lower southeastern slopes of Himalaya to temperate highlands of Hengduan Mts. Due to its particular physical geography, topography and geological history, rich biota has been evolved in the region, including diverse vegetation. In biogeography, Yunnan is a transitional area from tropical biota of SE Asia to subtropical and temperate biota of Himalayas and east Asia. The tropical rain forest with the similar physiognomy, structure and floristic composition to rain forest of SE Asia, occurs in southern Yunnan, and the subtropical evergreen broad-leaved forest, warm temperate deciduous, temperate coniferous-broadleaved forests occur in central and northern Yunnan, while cold temperate coniferous forest, subalpine and alpine shrubs and meadows in northern Yunnan. Besides, at the hot dry valleys of several large rivers and their tributaries, savanna-like vegetations occurs. Sclerophyllous and small-leaved forest and shrubs with Mediterranean affinity occur at warm dry valleys in northern Yunnan, while sclerophyllous oak forests occur all over Yunnan except tropical wet areas. The complicated patterns and diversity of Yunnan vegetation have been shaped mainly due to the particular geological histories, which are the differentia uplifts of topography, clock-wise rotation of Simao-Langping geo-block and extrusion of Indo-China geo-block with Himalaya uplift. Combined geological history, floristic geography, the origin and evolution of Yunnan vegetation could be understood.