Chinese Journal of Ecology, 2000, 19(1):23-31.Based on characteristics of Changes of food production and consumption level during recent 15 years, this paper designed a system model, defined some parameters and variables and carried out simulation study of food production and population capacity of the land in Gansu province by systems analysis. The population quantity that land can bear on four food consumption levels (poor, just enough, enough, good) in 2010 year in Gansu was given according to calculation of the two targets of capitation grain and non - staple food. The situation of population capacity was simulated when some variable factors such as population quantity, consumption level, changes of farm land, increase of irrigation area, input of industry energy, advance of science and technology in agriculture, and natural calamity dynamically changed. The characteristics and tendency of relationship between population and land changes was calculated for the coming 15 years. In view of the above, countermeasures and suggestions about harmonization of relationship between population and resources and realization sustainable development were put forward.