Abstract: This paper has evaluated the initial planting density and calculated suitable densities of the middle age Pinus sylvestris var. mongolica Litvin. artificial forest in Maowusu sand land. Using the gray system theory calculation,it is shown that suitable initial planting density of Pinus sylvestris var. mongolica Litvin. forest in sand land is 2m×2m(space).According to calculation result, meanwhile, the suitable density for middle age Pinus sylvestris var. mongolica Litvin. artificial forest in sand land is 3m×4m(space).