Soil crust has an important influence on water infiltration and erosion sediment production on slope, but its specific process and mechanism are still under debate. In this study, taking the alien soil slope in mining wasteland of Wula Mountain as the research object, the effects of soil crust on runoff and sediment were investigated by in situ scouring tests on the slopes with different slope lengths (2 m, 4 m, 6 m, 8 m and 10 m) and during flow and sand production process.The results showed that:(1) The total runoff and sediment yield on the 2 m slope increased significantly, which were 2.17 and 1.56 times of that on the control slope. The total runoff and sediment yield on the 4 to 10 m slopes decreased, and the total runoff was 67.17% to 78.45% of that on the control slope and the total sediment yield was 54.53% to 83.56% of that on the control slope. (2) The changes of runoff rate with time on the soil crust slope and the control slope were basically the same, showing a fluctuating and stable or slightly increasing trend. The sediment yield rate on the control slope showed a decreasing trend with time, while on the soil crust slope showed two trends of decreasing and stabilizing. (3) The relationship between cumulative runoff, cumulative sediment yield and runoff generation time could be expressed by linear function and power function. With the change of runoff generation time, the effects of soil crust slope on the accumulated runoff volume could be divided into three types:increase, decrease, increase firstly and then decrease. And the effects on the accumulated sediment yield could be divided into two types:increase and decrease. Therefore, the inhibiting or promoting effect of soil crust on process of runoff and sediment yield on the slope surface was closely related to the slope length and erosion occurrence process.