In order to find the suitable diameter distribution model for primary forest and secondary in Baisha County,Hainan Province.Five statistical distribution models:negative exponential model,limiting line model,logarithmic J-shape model,power exponential model and Weibull distribution model were selected and compared.The results showed that negative exponential model and Weibull distribution model are suitable models for modeling works,especially for the stem number of larger DBH classes in the tropical rain forests.