Based on simulated field rainfall experiment in the Beijing Mountain Area, this paper tried to analyze and evaluate the effects of the litter layer under artificial Platycladus orientalis forests on the runoff and sediment yield of the slope by comparing two kinds of treatment conditions (slope surface with litter coverage, and bare slope) under two rainfall intensities (126 mm/h, and 70 mm/h). The results showed that: (1) Compared with the bare slope, the runoff and sediment yield of the slope with litter coverage was significantly reduced by 67.0% and 90.6%, respectively. The benefit of litter layer on reducing the sediment was greater than that on reducing the water. (2) The runoff rate increased initially and then tended to be stable during the slope runoff process on the two types of slopes. Compared to the bare slope, the time for the runoff rate to be stable was shorter on the slope with litter coverage. (3) The average sediment transport rate under 70 mm/h and 126 mm/h rainfall intensity on the slope with litter coverage was 2.8 g/min and 80.8 g/min, respectively, which was significantly less than that on the bare slope with the value of 51.4 g/min and 872.7 g/min under 70 mm/h and 126 mm/h rainfall intensity, respectively. For the slope with litter coverage, sediment transport rate and sediment concentration did not significantly change with runoff duration, and the slope sediment transportation was a relatively stable process. For the bare slope, the sediment transport rate and sediment concentration increased initially and then tended to be stable under 70 mm/h rainfall intensity, while this change sharply increased initially and then decreased fluctuantly under 126 mm/h rainfall intensity. (4) There was a linear relationship between sediment and runoff yield on the slope with litter coverage, while the relationship was an exponent power function on the bare slope. Finally, this study can provide a theoretical basis for evaluating the benefit of plantation restoration in Beijing mountain area on soil and water conservation, and also improve the understanding of the process mechanism of runoff and sediment transportation on the slope of the forest.