Abstract: In order to investigate long-term effects of deep soil desiccation on yields of dryland apple orchards, and to determine suitable age limit of apple orchards on Loess Plateau, WinEPIC model was used to simulate water productivity and deep soil desiccation of dryland apple orchards during 1965-2009 at four sites on the Loess Plateau, which included Luochuan County of Shaanxi Province in semi-humid region, Baishui County of Shaanxi Province in semi-humid and prone-to-drought region, Yan��an City of Shaanxi Province in semi-arid region, and Jingning County of Gansu Province in semi-arid and prone-to-drought region. The simu-lated results showed as follows: in Luochuan, Baishui, Yan��an and Jingning, simulated yield of 1-45 years old apple orchards averaged 26.05, 23.89, 22.29 and 20.51 t/hm², respectively, and annual yield increased to a maximum at the earlier stage of growth, then followed by the tendency of decrease fluctuating with the local rainfall. In 1-20-year-old apple orchards,average annual water consumptions are higher than annual rainfalls, which resulted in desiccation in deep soil layers. In 1-22-year-old orchards of Luochuan, 1-21-year-old orchards of Baishui, 1-18-year-old orchards of Yan��an and 1-16-year-old orchards of Jingning, simu-lated monthly available soil water amounts in 0-15 m soil profile decreased rapidly with strong fluctuation. Soil desiccation rates in Luochuan, Baishui, Yan��an and Jingning were 59.6, 56.9, 63.9 and 64.9 mm per year, respectively, but they kept at a relatively low level and fluctuated with annual and seasonal rainfall changes at the later stage. The soil moisture in profiles varied sharply, the humidity declining annually. Dry soil layers occurred in the 13th, 11th, 7th and 6th year in Luochuan, Baishui, Yan��an and Jingning respectively, and the thickness of desiccated soil layer increased annually. In the 20-year-old orchards of the four sites, dry soil layers all have already exceeded 11 m in thick, and the soil moistures in 3-15 m layers remain steady after that. There were significant differences in water productivities and soil desiccation effects among the apple orchards at the four sites, and the soil water could be sustainably used by the apple orchards at the four sites for about 20-25 years.