Abstract: Overgrazing is an important reason for grassland ecological destruction in Qilian Mountains. In order to resumes and protects grassland ecosystem and constructs ecological animal husbandry in the northern slope of Qilian Mountains. In this paper, we selected the northern slope of Qilian Mountains in Sunan County as the study area, simulated the proper stocking capacity for livestock from different precipitation scenarios in grassland and analyzed the present forage-livestock balance status based on rotational grazing theory, researched the process of pasture production and demand with the proper stocking capacity in rotational pasturing area, carried out the dynamic forage-livestock balance analysis, and compared the result with the key pasture theory method and traditional method. The result showed that the change of precipitation greatly influences the proper stocking capacity for livestock of pasturing area in the northern slope of Qilian Mountains in Sunan County, the proper stocking capacity for livestock was 1.303 million sheep unit, 1.009 million sheep unit, and 65.1 million sheep unit in high, normal, and low flow years, respectively. In analysis of the proper stocking capacity for livestock calculated by three methods in different precipitation, we found that the result calculated by the traditional grassland-livestock balance method was the largest, and the result calculated by the grassland and livestock balance method based on key pasture theory was the lowest. This is because the traditional grassland-livestock balance method does not consider the relationship between the process of grassland production and demand of livestock in pastoral areas, the traditional grassland-livestock balance method does not consider the dynamic change of livestock number in the process of grassland demand of livestock. Therefore, we proposed that the proper stocking capacity for livestock in the normal flow year was 1.009 million sheep unit as the main reference indexes of animal husbandry management in the future. There were both existence overgrazing and under load problem in pasturing area in 2015, and the proper stocking capacity for livestock in cold season meadow was obviously different in warm, it should be adjusted to the current development of animal husbandry structure and rational allocation of cold and warm season meadow in the future. The proper stocking capacity for livestock calculated by the traditional grassland-livestock balance method would deplete the available forage in cold season meadow in March, which would lead to overgrazing. The proper stocking capacity for livestock calculated by the grassland and livestock balance method based on key pasture theory can ensure the dynamic balance of the grassland resources and livestock in the whole pasture area, but it produced a lot of waste of forage in the whole pasture. By contrast the results with the other two methods, the rotational grazing theory method not only can ensure the dynamic forage-livestock balance in different rotational pastoral areas, but also can maintain the efficient utilization of forage, and it showed that the rotational grazing theory method had certain superiority in analysis of forage-livestock balance in the rotational pastoral area. The results can provide a scientific basis for the restoration and protection of grassland ecology in Qilian Mountains and the development of ecological animal husbandry in Sunan County.