Abstract: Monsoon forest is a tropical forest-type, which part or most the upper canopy trees drought-deciduous during dry season of every year, or they are deciduous subdominant species in the tree crown. Monsoon forest is a forest-type of tropical climatic moisture gradient and a foresttype transition from tropical rainforest to tropical woodland. For this reason, the viewpoint of 《China Vegetation》 (1980), i. e. monsoon forest is the northeast type of tropical forest horizonal distribution, on the one hand it developing to tropical rain forest and on other hand also transition to subtropical evergreen broadleaved forest, were uncertain.Ficus formation and Endospermum formation in the lower subtropical region are not monsoon forests, they are the lower subtropical rain forests or the lower subtropical evergreen broad-leaved lowland forests. The single dominant Vatica formation is not monsoon forest but an edaphic climax of tropical rain forest in Hainan.