Abstract: The paper presented the characters of tropical forests and their secondary succession series in the Big Bend Gorge of Yalu Tsangpo River, S.E.Tibet, E.Himalayas. In the region the tropical forests occur in the bottom of the gorge at an altitude between 600-1200 m, which belong to the low mountain semi-evergreen tropical rain forests, and include mainly three types as follows: Altingia excelsa+ Terminalia myriocarpe forest; Altingia excelsa+ Lagerstroemia mimuticar pa forest and Altingia excelsa forest. The natural and artificial factors causing the destruction of the original vegetation were discussed. The factors led to two different secondary succession series of the semiuevergreen tropical rain forest.

Key words: Yalu Tsangpo river