Abstract:According to geographical and floristic components of forest,the floristie composition,properties and origin of the moist evergreen broad leaf forest at Xujiaba have been discussed emphatically in this paper. It was shown that this forest floristics was mainly consisted of Sino-Hima-layan, characterised by the endemic species in southeast of China,and comprised together with the north border component of tropical south eastern Asia (Indo-Malasia) in the shape of shuttle shown in its diagram of vertical structure,and also had a character of ancient origin. In addition,it had a closer relation with the south of Sino-Himalayan mountain forest and north of tropical southeast Asia,which had 5 layers and eight kind of synusia. Therefore,Xujiaba forest was the typical evergreen broadleaf forest at the top of the subtropical mountain vertical belt despite of the difference in ecological environment from other same mid mountain moist evergreen broadleaf forest.