In order to study the effect of slope and vegetation on the hydrodynamic characteristics of overland flow, a non-submerged rigid vegetation slope flow model based on the Navier-Stokes equation was established. The effectiveness of the model was tested by some experimental data. The calculated results were basically consistent with the experimental results. Based on the model and the actual situation of Southwest Mountain area, the hydraulic characteristics of overland flow were studied under 216 combined conditions of 6 slopes, 6 unit discharges, and 6 coverage degrees. The results showed that the relationship between flow velocity and slope, discharge and vegetation coverage is exponential, and the correlation is 0.987. Under the same flow, with the increase of slope, the growth rate of flow velocity decreased gradually, and the effect of vegetation on the slope flow slowed down gradually. The resistance coefficient was affected by slope, discharge, and vegetation cover, and there was a critical coverage. Below the critical coverage, the resistance coefficient was negatively correlated with discharge, and above the critical coverage, the resistance coefficient was positively correlated with discharge. The critical coverage was affected by the slope, the greater the slope, the greater the critical coverage. The results can provide theoretical reference for the prevention of soil and water loss and the study of the coupling mechanism of flood and sediment.