Abstract: This paper aimed at Zhangye city as a typical unit of northwest desert oasis area, its background of quality and quantity, actual productivity and potential productivity on land were analyzed. The results showed that water resources is insufficient under the condition of present water use efficiency, however, it could meet the needs completely based on the prerequisite by using efficient water-saving measures. Other factors relating to soil fertility levels, e.g. the content of organic matter, N and P, the bulk density of soil, etc., except for the decline of available K content year by year, demonstrated a successively improved trend for near 17 years even with conditions of high output and input. The productivity of farmland for major crops has attained to 73.4% of its potential productivity. In all cultivated plants, the net income of vegetables and reproduction of seed are，orderly，higher than those of forest products and various crops, those of vegetables by the intensive planting ways, e.g. Sunglow glasshouse or arch shed, higher than by plastic films. The key ways for raising population supporting capacity of land are the amelioration of water and soil environment, optimization of agricultural structure and strict control to excessive increase of population.