The “Valley-Savanna vegetation” is a special type of vegetation in mountane dry-hot valleys of southwest China. It has a special position in China, even within Asia. The composition, areal-types and floristic characteristics of seed plants in Yuanjiang Nature Reserve of Yunnan Province were studied on the basis of field survey. The results showed that there were 2 080 species of seed plants, belonging to 166 families and 835 genera, among of them 8 species are gymnosperm belonging to 3 families and 4 genera, and 2 072 species are angiosperm belonging to 163 families, 831 genera. The floristics of seed plants of Yuanjiang Nature Reserve is a transitional flora from tropical to subtropical area and with evident characteristics of tropical flora. The flora belongs to Sino-Himalaya subkingdom, Eastern Asiatic Kingdom. It is influenced by tropical Asian flora in origin and very rich in endemism (3 families endemic to East Asia, 5 genera and 647 species endemic to China).