[Objective] The regulating effects of soil bulk density and straw mulching on soil and water loss on slope cropland in the black soil region of Northeastern China were studied in order to facilitate further improvement and application of conservation tillage practices including no tillage and straw returning to fields. [Methods] Two levels of soil bulk density (1.2 and 1.3 g/cm³, representing the soil with conventional tillage and no-tillage practices, respectively) and four levels of straw mulching (0, 328, 656, and 984 g/m²) were considered in this study. For these treatments, simulated rainfall experiments were conducted. The starting times and rates of runoff generation as well as the amount of soil and water loss for each treatment were measured. [Results] ① Soil and water loss of the treatments with bulk density of 1.3 g/cm³ were significantly higher than observed for the treatments with bulk density of 1.2 g/cm³. Specifically, the starting time of runoff generation was reduced by 13.1%～49.9% by decreasing soil bulk density, and correspondingly the runoff and soil loss were increased by 0.4%～90.4% and 24.6%～302.8%, respectively, by the decreasing of bulk density; ② In comparision to the control (no straw mulching), straw mulching delayed the starting time of runoff generation by 1.2～2.9 times. Straw mulching also reduced runoff amount by 3.1%～38.9% and soil loss amount by 34.0%～97.9%. These decreases in runoff and soil loss were positively correlated (p<0.01, r=0.862) with straw mulching amount. The best performance of straw mulching in conserving soil and water would be obtained using 656 g/m² of straw mulch; ③ The soil and water loss on the black soil slope land was aggravated by increasing soil bulk density, but relieved by increasing straw mulching as a result of the straw returning practice. On average, no-tillage (increasing soil bulk density, 1.3 g/cm³) and straw mulching practices reduced runoff by 10.7% and soil loss by 74.2%. [Conclusion] In the black soil region of Northeastern China, no-tillage should be practiced in conjunction with straw mulching to prevent soil and water loss on slope cropland, and the optimum amount of straw mulching should be greater than 656 g/m².