Abstract: 【Objective】To clarify the soil bacterial composition,diversity,spatio-temporal distribution,response to soil physical and chemical properties and functional structures in tropical rainforests of Hainan Island,so as to provide a theoretical basis for the management and protection of the tropical rainforests in Hainan.【Method】Soil samples were collected from Diaoluoshan,Wuzhishan,Yinggeling,Bawangling and Jianfengling tropical rainforest reserves in Hainan. Thirteen samples were collected from each reserve in both the dry and wet seasons,producing a total of 130 samples. The composition and diversity of bacteria in soil microorganisms were analyzed with a high-throughput sequencing technique and the function of soil bacteria was predicted and analyzed by PICRUSt2 software.【Result】Operational taxonomic unit (OTU)classification statistics show that the number of bacterial OTU in the dry season is 10958 and that in rainy season this increases to 11533. There was no significant difference between the two seasons(P>0.05). At the level of bacteria phylum,the dominant flora of soil bacteria in tropical rain forest in dry season and rainy season were Proteobacteria,Acidobacteria,Actinobacteria,Planctomycetes and Verrucomicrobia. The abundance of Bacteroidetes,Actinobacteria and Cyanobacteria in two seasons showed significant differences(P<0.01,the same below). At the level of bacterial class,the dominant classes in the dry and rainy seasons were Actinomycetia,Acidobacteriia,Alphaproteobacteria,Planctomycetia and Spartobacteria. There were significant differences among the classes Planctomyceteria,Sphingobacteriia,Ktedonobacteria and Actinomycetia. Redundancy analysis(RDA)showed that pH and total potassium(TK)affected the soil bacterial composition substantially,with explanation rates of 5.03% and 4.28% respectively. ANOSIM and Adonis analysis showed that there was no significant difference in bacterial diversity in the different seasons,but significant difference in bacterial diversity in different places. KEGG pathway showed that the bacterial functional abundance in the Diaoluoshan samples was less than that from the other four reserves.【Conclusion】The diversity of soil bacteria in Hainan tropical rainforests is significantly different in different geographical locations(sampling sites),whereas the seasonal change does not affect the composition of soil bacteria significantly. Soil pH and total potassium(TK)content have important effects on the soil bacterial diversity in the dry and rainy seasons.