There are many different factors affecting overland flow, such as climate, geology and vegetation, among which vegetation type is a key factor. In this study, four different vegetation types in J inyun Mountain, Chongqing City, were investigated using the grey rational degree. The analyses of precipitation and vegetation ef2 fect s on overland flow indicate the highest rational degree of precipitation with surface runoff. The parameters contribute to overland flow in the descending order of canopy density, standing foresTheight, litter thickness, slope degree, coverage and soil thickness. The rational degrees of different vegetation types descend in the order of mixed wood, broadleaved forest ry, bamboo forest ry and cropland.