A field experiment was carried in Yangling using simulated rainfalls, designed to have two rainfall intensities (1.5 and 2.0mm min^-1), on slopes of Lou soil, different in gradient (10°,15°,20° and 25°), to study characteristics of rill development and distribution of flow velocity along the slopes. Results show that slope gradient is positively related to rill density and average depth of the rills, but with the increase in slope gradient, the increment of total erosion rate tends to level off in amplitude, which implies that there is likely a threshold slope gradient where soil erosion begins to turn from strong into weak. Slope gradient shows extremely significant relationship with to the various indices of soil erosion, indicating that slope gradient is the major factor affecting development of rills. Rill erosion rate is also found to be closely related to total erosion rate, with correlation coefficient being 0.97, indicating that the aggravation of soil erosion on the slope is caused mainly by rill erosion. Flow velocities on the slope, in and in-between rills are all positively related to their distances to the slope top. Rainfall intensity intensifies fluctuation of the trend. However, slope gradient does not have much influence on flow velocities on slopes, in and in-between rills and, moreover, no significant relationship is found between these flows in velocity, which is contradictory to the general conclusion that flow velocity is higher in rills than in-between rills, and remains to be further verified in future experiments.