We apply the gaging weir approach to make the research on the amount of soil erosion under the original subtropical mountainous evergreen broad-leaf forest of a small watershed in the Jiu-lian mountain reserve,Jiangxi province.This small watershed is of the steeper type and its area is 14. 4 ha. In the five years from 1986 to 1990 , we got some results of the observation and survey of the soil erosion in the region. The annual sediment deposited in the silt trough of the gaging weir is about 530-1820 kg. The annual solid flow from the notch of the weir is about 70-330 kg/ha,and the organic matter makes up about 15% of the whole erosion amount.We make an analysis on the basis of the results of observations, and find out that the annual erosion amount mainly depends on the precipitation intensity. The annual erosion amount will markedly increase in the year when there are rainstorms and more intensive rains. Because soil erosion is mainly caused by surface flow, but the water permeability of the soil under the evergreen broad-leaf forest is very good.and about 97% of the precipitation in the small watershed can permeate into the soil,therefore the erosion amount under the evergreen broad-leaf forest in the small watershed is little.