The purpose of this study is to investigate the effects of rainfall erosivity index AI on the hydraulics of overland flow parameters such as the flow velocity, the flow depth, the flow regime, overland flow power and on soil surface characteristics, such as surface roughness and sediment concentration. The erosivity index AI represents six rainfall intensities, 31.40 mm·h-1; 37.82 mm·h-1; 69.49 mm·h-1; 81.85 mm·h-1; 90.39 mm·h-1 and 101.94 mm·h-1 generated by a rainfall simulator. To simulate the soil plot, a soil tray was filled with remolded agricultural sandy soil. The results found have shown that the AI represents better the rainfall than rainfall intensity and related to drop diameter with a power function. Overland flow never exceeded the laminar and subcritical regime; the Reynolds number reacted differently with AI and rainfall intensity, whereas the Froude number has similar reaction with both parameters. Re, Fr and n follow with AI logarithmic, linear and power functions respectively. Finally, AI is a good predictor of soil erosion.