Abstract: Though conducting rain simulation experiments which used deionized water under different slopes (10°, 15°, 20°, 25°), different slope lengths (5, 10 m) and different rainfall intensities (90 mm/h, 120 mm/h), the distribution of flow velocity and the relationship between it and sediment concentration were discussed. From the top of the slope to the foot, the flow velocity gradually increased; and it was mainly affected by rainfall intensity and the distance it flew, while it was independent of slope, a simple equation was obtained. Relationship between velocity and rainfall intensity and the distance from the top was acquired. The results showed that sediment concentration was dependent of gradient slope, rainfall intensity and flow velocity, however sediment concentration measured of the 10 m slope was similar to that of 5 m slope. The energy of overland flow can be divided into three parts: the energy needed for its own mobile, the energy consumption of soil erosion and the energy needed to bring the soil particles. Within certain slope lengths, the energy of flow was enough for soil erosion and transport. Beyond this distance, although velocity of flow increased, the removal of sediment would consume more energy, so that there would not be more energy for the erosion of soil, thus sediment concentration didn’t increase significantly.