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Mean flow velocity is one of the most important hydraulic variables in soil erosion modeling, which is normally estimated by multiplying surface velocity of flow with a correction factor (α). So a reasonable α value is imperative for precise estimation of mean flow velocity. The effects of grain resistance, transport resistance and vegetation resistance on correction factor α were investigated through indoor scouring experiment on the basis of the datasets collecting from the literature. The results showed that α decreased as grain resistance, transport resistance increased and increased as vegetation resistance increased. The effects of different resistance forms on α were mainly achieved by changing the velocity profile of overland flow. The grain resistance and transport resistance made the velocity profiles steeper, while the vegetation resistance made the velocity profiles gentler. The prediction equation of α under various forms of resistance was proposed by using stepwise regression analysis and the predicted values agreed well with the measured ones.