Abstract:The tropical seasonal rain forest of Xishuangbanna is one of the typical tropical rain forest of China. The study has been made on the floristic elements of Pometia tomentosa forest community, a very widely distributed and representative type in Xishuangbanna. There are 83 families, 181 genera and 236 species (including 98 tree species) distributed in a 0.25 hac area. The taxonomy, geographic characteristics, ecological components and historical components of the community have been studied and analysed. The results indicate that this community type has a typical characteristics of Southeast Asia tropical rain forest, and the floristic elements reflect the connection and identical characters. The ecological analysis reflects its inclined dry characters , which is caused by the southeast seasonal wind from South Asia. The historical analysis reflects that this community has resulted from very ancient and different forms.