Abstract: The hydrochemical properties, seasonal changes and their balance of both semi-deciduous monsoon forest-latosol-granodiorite, granitite and mountain rain forest-lateritic yellow soil-potassium feldspar granite systems were studied at Jianfengling, Hainan Island, China based on the observations and chemical analyses on the major elements of precipitation, throughfall and stream. Elements content of the throughfall increased by 0.3~2.8 times more than that of the precipitation. More leaching quantity was found in the semideciduous monsoon forest than that of the mountain rain forest particularly K and N the most, and the leaching loss of Ca was less than the surface uptake of the plants in the mountain rain forest. The elements content of the stream were also less than that of the throughfall. The output content is more than input both in the Si, Ca, Mg and dried residue for the semi-deciduous monsoon forest and the Si, total acidity and total alkainity for the mountain rain forest. There are obviously seasonal changes in various hydro-elements content with seasonal changes of rainfall and forest plants and solubility of elements. It is pointed out that the precipitation and throughfall are an input source of the important elements of the tropical forest ecosystem, which has stronger function on the filtration, uptake and store. It is clear that hydrochemical regulating function of the mountain rain forest ecosystem is superior to that of the semi-deciduous monsoon forest ecosystem.