By adopting the revised WinEPIC model, a simulation study was conducted to investigate the responses of the apple yield and deeper soil moisture content to 7 planting densities in the apple orchards in Yan’an of Shaanxi and in Jingning of Gansu in 1965-2009. Under the 7 planting densities, the annual yields of the 4-45 years apple orchards increased rapidly at early growth stage, and then decreased with fluctuation after reached the maximum. The higher the planting density, the higher the annual yield was obtained at early growth stage, but the yield at late growth stage fluctuated dramatically with annual precipitation. The orchards with different planting densities had the similar soil water stress process, i.e., no water stress at early growth stage, and water stress occurred and fluctuated dramatically with increasing planting years. The days of water stress at late growth stage changed oppositely to annual precipitation. At early growth stage, the soil available moisture content in 0-15 m layer under the 7 planting densities all decreased rapidly with strong fluctuation, ranged in a low level of 0-600 mm after 17-22 years in Yan’an and after 13-20 years in Jingning. The soil moisture content in 0-15 m layer changed similarly under different planting densities, i.e., decreased gradually with the deepening of soil desiccation, and the stable depth of drying layer could reach 12 m. Considering the apple yield and the soil available moisture content in 0-15 m layer, the reasonable planting density of apple orchard was 650-800 plants·hm^-2 in Yan’an and 550-700 plants·hm^-2 in Jingning.