Through multi-stage simulated rainfall experiments with different rain intensities and slopes, the slope and slope erosion modulus are fitted with quadratic polynomials to obtain the critical slope of slope erosion under different conditions. The experimental results show that the critical slope will change regularly with the change of rainfall intensity and rainfall duration. The greater the rain intensity, the greater the critical slope, and the stronger the impact on the critical slope of slope erosion. As the rainfall duration increases, the critical slope of slope erosion also increases. The greater the rain intensity, the faster the critical slope growth rate and the earlier the inflection point of the growth rate appears. In the initial stage of slope erosion, the slope increase strengthens the transport effect of slope runoff on the slope surface sediment and weakens the splash erosion effect of the slope surface, so that within a certain slope range, the onset of rill erosion on the slope surface with a large slope is later than the slope slope，which is one of the reasons for the critical slope. With the development of slope erosion process, slope erosion mainly occurs on the edges, sidewalls and bottom of rills. The difference in erosion modulus per unit time of slopes with different slopes decreases and tends to stabilize. The impact gradually decreases, and the critical slope gradually disappears. This study can provide a theoretical basis for improving the mechanism of soil erosion in the loess area.