The general floristic characteristics of the tropical rainforest of Xishuangbanna have been summarized in the present paper. The tropical rainforest is estimated to consist of more than 3,000 species of seed plant pertaining to more than 1,000 genera and about 180 families. Based on the comprehensive analysis of the distribution of taxa in two representative communities of the rainforest, the deduction is given as follows: the families, genera and species of tropical distribution take up about 80%, 94% and more than 90% of the total of the flora separately in which the genera of tropical Asia take up 33%–42% of the total and the species of tropical Asia take up about 74% of the total. The flora is explicitly of tropics in nature and as a part of tropical Asian flora. Occurring at the montane habitats of northern margin of tropical SE Asia, the flora also embodies conspicuous characters of marginal tropics. Xishuangbanna is geographically a transitional area from true tropics to subtropics and an ecotone where the floristic element of Indo-Malaysia from south, the one of S Asia or S Himalayas from west, the one of Indochina-S China from southeast and the one of S China from northeast meet and overlap in their areal boundaries each other. The flora is therefore endosed with the characteristics of floristic ecotone.