According to the statistic data of XilinGol pastoral from 1981 to 2013,based on the theory of supply, the empirical models for the sheep grazing capacity were built by C - D function,and the factors influencing the inventory quantity of sheep in research area were analyzed. The results showed: 1) The cost of feeding sheep and the strengthened grassland management policies had significant negative impacts on it. Strengthened grassland management policies made the number of overgrazing sheep decrease on freely grazing grassland area. In order to avoid falling of incomes,herders turned to confinement and semi confinement from freely grazing which caused feeding cost to increase. On the basis of revenue maximization in the period,herders lowered it to realize the aim of rearing costs minimize. 2) Mutton prices had a significant positive impact on the inventory quantity of sheep; with the mutton price increasing,perhaps herders expected the mutton price continuously increase next year,so they increased the inventory quantity of sheep to prepare in order to maximize next income. 3) Annual precipitation had positive impact on the inventory quantity of sheep. Annual precipitation increasing made grassland well, the feeding cost decreased,and the inventory quantity of sheep increased. Under the surrounding of global warming, introduction of grassland policy and improving sheep earning were the main means to reduce inventory quantity of sheep.