Erosive rainfall standard refers to the critical value of rainfall differentiating the occurrence and no n-occurrence of erosion by individual rainfall. The determination of the standard can judge whether or not individual rainfall leads to soil erosion and soil nutrient loss. Based on the observed data from slo pe cropland runoff plots,its found that slope gradient has a sig nificant impact on the number of erosion events in the same time series (correlation coefficientr=0.968) and the standard of erosive rainfall in the purple soil area of M id-Sichuan is drafted. The precipitatio n standar ds of erosive rainfall for 5,10,15,20,and 25 slopecro plands are 55.7,42.9,39.9,39.5,and 32.0 mm; the average rainfall intensity standards, 8.87,7.86,5.53,5.36,and 5.24 mm/ h;and the PI standards, 552.12,416.16,351.09, 331. 53, and 239. 29 mm²/ h,respectively. T he relationships betw een precipitation standar d and slope gradient, average rainfall intensity standard and slo pe gradient, and PI standard and slope gradient are fitted by regression analysis.