Taking the Jiuquan City, Guansu Provice, China as an example, according to the 1997-2007 Gansu Statistical Yearbook, Jiuquan Statistical Yearbook, the Second National Land Investigation in Jiuquan City and other relevant statistical data, models of minimum cultivated area per capita and pressure index of cultivated land are used based on food security. Cultivated land area, population, grain output, sowing area and other factors in years 1997-2007, which affect the cultivated land pressure in arid and semi-arid areas, are analyzed and estimated, as well as the temporal variations of minimum cultivated area per capita and pressure index of cultivated land. Pressure index of cultivated land in Jiuquan City is calculated and the pressure situation of cultivated land at present is analyzed. Based on the construction of demand function of cultivated land, demand of cultivated land, that is, the protected area of basic farmland and cultivated land, is finally obtained so as to achieve the goal of food security in Jiuquan City at the stage of comprehensive construction of a well-off society in the year 2020. Considering the food security of China, we use PSR Model and find out that it is necessary to strengthen government’s macro-control functions, to protect the fragile ecological environment, to improve the land intensive and economical use during the process of urbanization, and to reduce the pressure of cultivated land in arid and semi-arid region, and to provide theoretical basis for the policy making of cultivated land protection in this region.