Abstract:Applying the method of size structure, this paper studies the population dynamics of constructive species of the tropical montane rain forest in Xishuangbanna. In the overstory, size-structure of constructive species Nephelium chryseum is an increasing population which will maintain relative stability over a long period of time. Winchia colophylla papulation has seedlings and saplings, but is short of young trees. Paramichelia baillonii population is short of seedlings and saplings, and is hard to reproduce itself in the dense shade of a forest or tree gap. It appears to be a senescent population. Paramichelia baillonii, Schima wallichii population is short of seedlings and saplings, but it may reproduce itself under tree gaps.