Abstract: Species richness-abundance relationships in four types of tropical forest (tropical submontane rain forest, tropical montane rain forest, tropical cloud forest and tropical dwarf-forest) were studied at Bawangling National Nature Reserve, Hainan. Four size classes of tree with diameter at breast height (DBH≥1.5, 10, 30 cm respectively) were selected for comparison. The results indicate that the rate of species accumulation is related to the logarithm of number of individuals in each vegetation type, independent of diameter classes. Within samples containing the same number of individuals the rate of species-accumulation decreased from the tropical submontane rain forest, through tropical montane rain forest and tropical cloud forest to the tropical dwarf-forest. For each vegetation type, the proportion of rare species (singleton or doubleton: observed just one or two times respectively in samples) is very high. Their proportion is about 50% of the total species counted in each DBH classes and increases with diameter class. On the other hand, the proportion of species with hundreds of individuals is very low, usually under 1%.