Abstract: To further realize the correlation between rainfall and the starting mechanism of the slope debris flow in the source area of Yindongzi gully, a typical model was selected after a detailed fieldwork and engineering investigation. The rainfall intensity and gradient were set as control variables using 20 large artificial rainfall physical model tests under four gradients and five rainfall intensity conditions to research the instability mechanism and failure patterns of the slope debris flow. The experimental results revealed the starting and failure model of the source of the loose slope and the response relationship of the surface deformation and the underground physical mechanical parameters. Then, a traditional I-D (rainfall intensity-duration) early warning model was established. Next, reliable warning parameters (i. e. gradient and moisture content) were extracted and the exponential model and means of the mathematical regression analysis were used to determine the IGD and IGM multi-parameter forecast model, while the traditional model was effectively modified for dependability and practical utility.