In order to compare the effects of Astragalus adsurgens Pall. and Medicago sativa L. on reducing runoff and sediment, we set up three rates of flow (1 m3/h, 2 m3/h, and 3 m3/h), and five kinds of vegetation coverage (100%, 75%, 50%, 25%, and 0%). The submersible pump was used to carry out the runoff scouring experiment. The results show that: (1) The permeability coefficient of the slopes on which A. adsurgens and M. sativa were planted was larger than that of the control group, but the runoff and sediment of the slopes on which A. adsurgens and M. sativa were planted was less than that of the control group, indicating that A. adsurgens and M. sativa having effects on runoff and sediment reduction. (2) The effects of A. adsurgens on runoff and sediment reduction were better than that of M. sativa in the northern mountain area of Beijing. For example, compared with the control group, when the flow rate was 3 m3/h, the permeability coefficient of the slopes on which A. adsurgens and M. sativa were planted was increased by 5.8% and 45.3%, respectively. Total runoff of the slopes on which A. adsurgens and M. sativa were planted was less than that of the control group, being decreased by 3.7% and 11.2%, respectively. Sediment yield of the control group was 6.40 and 9.19 times the size of that of the slopes on which A. adsurgens and M. sativa were planted. The effects of A. adsurgens on slope infiltration and sediment reduction were better than those of M. sativa. (3) There was a critical phenomenon in the effect of vegetation on sediment reduction. The critical coverage of herbaceous plants for sediment reduction in this region was 50%-75%.