Abstract: The characteristics and distribution of tropical vegetation types in the Jianfengling Mountain of Hainan Island have been discussed in this paper and it was found that the distribution was determined by elevation above sea level and the variation of water-heat regime. The vegetation of this region consists of several types, namely littoral thorn thickets, shrubby grassland, tropical deciduous monsoon forests, tropical evergreen monsoon forest mountainous rain forest and dwarf mountainous woodlands. With a tropical monsoon climate, the sunshine duration of the region is long. Generally it has 1632 to 2623 hours per year, so solar radiation is plenty and more than 12.0 to 14.0 kcal/cm per year. It is warm all the year round.The relationship between the water-heat regime and the distribution of tropical vegetation is a linear, index equation, i.e.:(a) Q=13.43–21.3H, where Q is total solar radiation. H is altitude above sea level with a correlation coefficient r= –0.84 and (b) T=25.0–0.006H r= –0.99,T is average temperature with a correlation coefficient.The precipitation of 1300 to 3000mm per year is higher than that in the nearby region.In low-altitude districts there is an obvious dry season, while in other districts water is abundant owing to the precipitation brought on by typhoons. Precipitation (R) increase with altitude is an index law: R= 1276.4e0.0009H r= 0.91.Therefore, the water-heat regime and the vertical distribution of tropical vegetation are closely related.