[Objective] The erosion mechanism of colluvial deposits was researched to provide a theoretical basis and scientific evidence for the treatment of collapsing hills.[Methods] An indoor rainfall simulation experiment on slopes of colluvial deposits under 90 mm/h rainfall,and with the treatments of coverages(0,25%,50%,75%,100%) and slopes(25°,30°,35°) was carried out. Runoff and sediment were measured.[Results] The initiating time of runoff under different conditions changed from 33 to 292 s. Under the same slope gradient, there was a linear positive correlation between the initiating time of runoff and the straw coverage, and the initiating time of runoff had a power function with slope as independent variable. Through two-way variance analysis, the influence of slope on runoff was very significant and the influence of coverage on sediment yield was significant. The critical straw coverage of sediment yield was 50% under 25°, the critical straw coverage of sediment yield was 75% under 30°, the critical straw coverage of runoff was 50% under 35°.[Conclusion] For different slope gradients of colluvial deposits,we can choose optimal coverage of straw to reduce sediment yield and runoff effectively.