Abstract：Resistance to flow of surface water determinesthe study hydrodynamics in the slope. The common resistance types in the wild are grain resistance that mainly exerted by soil particles,and thevegetation resistance that exerted by the vegetation belonging to form resistance. However, there are no consensus conclusions about the laws of overland flow that influenced by the grain and vegetation resistance, especially for the resistance to overland flow that calculated by manning’s resistance coefficient. Simultaneously, the superposition principle that used to calculate composite resistance needs to be verified in these situations for the overland flow. Therefore, the artificial scouring experiments in the fixed bed have beenconducted at the slope gradient of 5° in Jinyun Forest Ecosystem Research station, Chongqing Province, China. The waterproofs with different roughness were selectedto simulate the surface roughness, whilethe circular cylinders with different diameterswere used to simulate the vegetation coverage. In this study, 9 different unit discharges varyingfrom 0.2´10-3 to 0.5´10-3 m3/(m ·s) were set as the water inflow; 3 different grain sizes ks of surface roughness of 0.12, 0.18, 0.38 mm were selected to simulate the grain resistance, while the ks of smooth flume bed equaled to 0.009; and 4 different vegetation coverage Cr of 0, 4.0%, 6.6%, 12.2% were selected to simulate the vegetation resistance. To calculate more accurately, the resistance was calculated by the equivalent manning’s resistance coefficient ne which usedthe equivalent hydraulic radius, instead of hydraulic radius. The equivalent hydraulic radius were considered the contact area of vegetation and flow, while the hydraulic radius did not. The velocity of overland flow were measured using a trace method, and repeated for 10 times. Afterwards, the flow depth h and n ewere calculated. Results showed that 1) the ne negatively relates with discharge for non-vegetated slope, while positively relates with discharge for vegetated slope. The ne increases as the increasing ks and Cr. 2) Assuming the composite resistance equals to the sum of grain resistance and vegetation resistance, the equivalent manning’s resistance caused by grain resistance neb and caused by vegetation resistance nevcan be deduced. The neb negatively relates with h, while positively relates with ks. The n ev linearly positive relates with h for larger h, while the nev is larger for the lower h. This phenomenon indicates that the linear superposition principle wasnot suitable for calculating the overland flow resistance, because the vegetation resistance should be linearly positively related with h for the fully flow depth if the linear superposition principle was suitable based on the results of previous works. The larger nev for the lower hcan beattribute to the effect of additional resistance. Because of the shallow flow depth of the overland flow, the region impact of surface roughness was overlapped with the region impact of vegetation. Therefore, twotypes of the resistance interfered each other, resulting the additional resistance. Afterwards, the equivalent manning’s resistance that caused by additional resistance nawas used to verify nev, resulting in nev linearly increased as the increasing h. The na negatively related with h, while positively related with ks and Cr. 3) The multiple regression analysis was used to simulate ne, and the results was well accordance with the observed ne (correlation coefficient 0.98). Finally, by comparing correlation coefficient R after rejecting corresponding resistance components, the vegetation resistance is the major factor of ne and the grain resistance is the second major factor, while additional resistance has the smaller impact on n e. This finding provides sound supports for building the model of soil erosion, and for the conservation of soil and water on the slope.