The rules of soil erosion processes influenced by slope length were studied using the simulated artificial rainfall experiments. The results show that slope length is an important factor that influences runoff and soil erosion. There is significant linear relationship between runoff and slope length, and there is a exponential relationship between soil erosion and slope length. The accumulation of both runoff amount and soil erosion increases linearly with rainfall duration and the increment increases with rainfall intensity. The slope length is also important for the evolvement of erosion configuration. Under the experimental condition, when the rainfall intensity is 0.72 mm/min, rill erosion cannot occur on 2.5m long plot, 5m long plot, 7.5m long plot and 10m long plot; when the rainfall intensity is increased to 1.14mm/min, rill erosion occurs on the 10m long plot; when the rainfall intensity exceed 1.14mm/min, rill erosion occurs on the plot longer than 7.5m. Once the rill develops, the runoff, soil erosion and sediment concentration will increase rapidly.