The variation of soil microbial community structure along the altitudinal gradient is an important content of microbial biogeographic differentiation and community spatial distribution. However, the altitudinal pattern of soil microbial diversity and its community characteristics in tropical forests is not clear. This paper studied the changes of bacterial diversity and community composition and their relationship with environmental factors in 0-20cm and 20-40cm soil depths along the altitudinal gradient (400-1410 m) in Jianfengling Nature Reserve, Hainan Province. The results showed that the soil microbial biomass carbon, biomass nitrogen and biomass phosphorus increased with the elevation of 0-20cm (the peak decreased), and the soil microbial biomass carbon, biomass nitrogen and biomass phosphorus increased first and then decreased with the elevation of 20-40cm. On the whole, Proteobacteria, Actinomycetes, Acidobacteria, Bacteroidetes and Firmicutes are dominant in 0-20cm, and the total abundance accounts for 88.17% of the total bacteria in this layer; Proteobacteria, Actinomycetes, Acidobacteria, Firmicutes and Chloroflexi are dominant in 20-40cm, and the total abundance accounts for 90.82% of the total bacteria in this layer. With the increase of altitude, the bacterial diversity decreased linearly in 0-20cm, and that of 20-40cm did not change significantly. The bacterial community composition of 0-20cm can be divided into three communities at low altitude (409-1018 m), medium altitude (1018-1357 m), and high altitude (1410 m) and the bacterial community composition of 20-40cm has no significant change with altitude. There was a significantly positive correlation between bacterial diversity and soil pH in the two soil depths. The composition of soil bacterial community was mainly affected by mean annual temperature and pH at 0-20cm, and by mean annual temperature and soil organic carbon at 20-40cm. According to the Bray Curtis index, the similarity of bacteria in 0-20cm and 20-40cm soil depths decreased with the increase of geographical distance, and the similarity of bacterial community also decreased with the increase of environmental distance. In a word, the altitudinal pattern of soil bacterial diversity and community composition in Jianfengling is affected by soil depth, and the factors driving the change of bacterial community composition are different among soil depths. It is suggested that the soil microbial communities in 0-20cm and 20-40cm of tropical forests may have different response mechanisms under the background of future climate change.