Abstract: In this paper, the analysis on the character of precipitation in Hainan Island shows that the annual rainfall is large with an apparently uneven distribution over whole region. The rainy season and dry season is distinguishable in a year and annual rainfall differs obviously year by year.The seasonal variation is small for the amount of precipitable water in the atmosphere but is large for the flux of water vapour.Computational results of surface run-off shows that the water storability on this island is small due to its topoghic feature, a mountainous centre and flat surrounding, which reaults In many short rivers divergent. Hence the surface run-offbehaves similar feature to the rainfall causing flood and/or drought deposit elsewhere.Two factors, the influence of weather systems and the topographic effect, are responsible to the creation of such precipitation feature.Finally, the relationship between the precipitational feature and the economic development in Hainan Island is analysed. Some rational suggestions such as drought-resisting conservancy,living creature resource protection, and efficient utilization and development of energy resources etc. are presented.