In order to study the effects of different planting densities on soil erosion of sloping cropland under the conventional tillage, different planting densities and growth periods of winter wheat were used to simulate the different crop coverages. The artificial rainfall simulation method was used to measure coverage, surface runoff and soil erosion of five different density treatments (0, 1 500 000, 2 500 000, 3 500 000 and 4 500 000 plants/hm²) in different growth periods, and to analyze the effect of crop coverage on soil erosion. The result showed that: (1) The difference of crop planting density on sloping cropland lead to the difference of coverage, which had a significant impact on soil erosion. Crop coverage generally increased with the increasing of planting density, however, if the density was too high, due to poor growth conditions, the coverage became smaller. The coverage was the largest at 75 000 plants/hm², but the coverage of 90 000 plants/hm², which was the highest planting density, was not the largest. (2) There was a good exponential function relationship between erosion and runoff and crop cover, and the function was Y = 44.37e^-0.09x (p < 0.01), Y = 1089.19e^-0.02x (p < 0.01), respectively. That is, with the increasing of crop coverage, runoff and erosion decreased. (3) There was a significant exponential function relationship between soil erosion and surface runoff (R² = 0.96). These conclusions were of great significance for analyzing soil erosion in conventional tillage cropland, quantifying the factors of tillage measures, accurately predicting soil erosion, and guiding cropland water and soil conservation.