The uplift of the Tibet Plateau resulted in large-scale Gobi and deserts in Northwest China,in which the fine particles finer than 0.1 mm were transported to and deposited in the region of the Loess Plateau by wind, and then formed the loess of a great thickness. The body of loess deposition can be viewed as a giant lenticular structure named “Loess mantle”. According to the process of loess deposition, it can be divided into four subregions: the transitional zone, the stable zone, the marginal zone and the long-range zone of loess deposition. Primarily the long-term climatic changes caused the gully erosion in the stable zone. This paper aims to re-establish the stops of the gully development using the geological records of the gully system on the Loess Plateau and to establish the mathematical model of soil erosion. With this mathematical model the natural erosion module has been calculated as 10 250 t/km2.a for the Ausal area of Shaanxi Province. However, the actual erosion module is 15,000 t/km2.a because about 31 .6% of the total erosion is created by human activities. The uplift of the Tibet Plateau resulted in large-scale Gobi and deserts in Northwest China, in which the fine particles finer than 0.1 mm were transported to and deposited in the region of the Loess Plateau by wind, and then formed the loess of a great thickness. The body of loess deposition can be viewed as a giant lenticular structure named “Loess mantle”. According to the process of loess deposition, it can be divided into four subregions: the transitional zone, the stable zone, the marginal zone and the long-range zone of loess deposition. Primarily the long-term climatic changes caused the gully erosion in the stable zone. This paper aims to re-establish the stops of the gully development using the geological records of the gully system on the Loess Plateau and to establish the mathematical model of soil erosion. With this mathematical model the natural erosion module has been calculated as 10 250 t / km2.a for the Ausal area of ​​Shaanxi Province. However, the actual erosion module is 15,000 t / km2.a because about 31 .6% of the total erosion is created by human activities.