Tropical montane rain forest (TMRF), one of the primary forest vegetation types in Xishuangbanna, occurs at lower altitude in the north (TMRF I) and higher altitude in the south (TMRF II). In order to understand the plant diversity characteristics of tropical montane rain forests in different zones, six permanent plots (50 m×50 m) of tropical montane rain forest communities at different sites in Xishuangbanna were established, two of which were in the TMRF I and four in the TMRF II. The grid method (10 m×10 m) was used to record all individuals with a DBH greater than 2.0 cm in each plot. Shrub and herb species were investigated in nine 5 m×5 m and 2 m×2 m sub-quadrats, respectively. Plant diversity indices of trees, shrubs, herbs, and three sub-tree layers, and changes in plant diversity indices of communities along the altitudinal gradient were analyzed. The results showed that the total number of plant species in the TMRF communities were 99-181, tree species richness (S) was 54-113, Shannon-Wiener diversity (H′) was 1.648 7-4.049 1, Simpson index (λ) was 0.503 5-0.969 5 and Pielou's evenness index (Jsw) was 0.413 3-0.854 9. For shrubs, S was 35-89, H′ was 2.413 2-3.716 2, λ was 0.762 7-0.958 2, and Jsw was 0.678 8-0.859 3. For the herbs, S was 31-65, H′ was 2.792 1-3.499 2, λ was 0.902 0-0.938 2, and Jsw was 0.729 3-0.838 2. The diversity indices, H′, λ, and Jsw, were greatest in the herb layer followed by shrubs and then trees, whereas species richness showed no obvious differences in the TMRF I. For TMRF II, the species richness and diversity indices, H′ and λ, were greatest in the tree layer followed by the shrub layer and then the herb layer, but the evenness index (Jsw) was not different among the three layers. The species richness, diversity indices and evenness index of the tree layer and shrub layer in TMRF II communities were higher than those in TMRF I communities, most likely due to the superior habitat of the TMRF II communities. Along the altitudinal gradient, all indices (S, H′, λ, Jsw) were greatest at the mid-altitudinal zone (about 1 200-1 220 m) for trees. This can be attributed to the fact that TMRF communities in the mid-altitudinal zone are situated in a ravine area and have the most favorable growing conditions among the six plots. Furthermore, these communities are very near to the seasonal rain forest at lower altitudes, and thus the tropical rain forest plants are very abundant at these altitudes.