Abstract: Based on the technique of small watershed and the method of permanent observation plot, the runoff yield had been studied in the regenerative tropical mountain rain forest at Jiangfengling, Hainan Island. The results indicated that the total annual rainfall, runoff, quickflow and surface runoff were 2881.5, 1282.1, 321.6 and 26.8mm respectively, and the annual runoff coefficient and hydrologic response were 44.5% and 11.2% in the hydrologic year from May 1989 to April 1990. It was found that the surface runoff was far less than the baseflow, the former only 2.1% and the latter up to 74.9% in the annual runoff. The authors pointed out that there are three typical types of storm-runoff hydrograph and that main runoff pattern is saturated runoff formation in the forested watershed. According to the analysis of runoff, it was considered that the regenerative tropical mountain rain forest has a good hydroecological effect on reducing flood peak discharge, delaying flood period and increasing runoff in dry season.