Abstract: Cultivated land is the core of land, and is an important factor to ensure food security. In allusion to the disadvantage in the former research, the paper, taking Rong chang County of Chong qing as an example, analyzed the change of cultivated land area and its causes from 1996 to 2004,and the results shows that; (1)Area of cultivated land has changed a lot, the total area of cultivated land and per capita cultivated land has been reduced year and year;(2)There are great regional differences in cultivated land change, and the cause is different;(3)Conversion of cultivated land for ecological use is the main cause of county reduction in the recent 8 years, and meanwhile conversion from cultivated land into construction land can realize requisition and compensation balance of arable land through land consolidation;(4)Reduction of cultivated land for construction land every year has been ill correlated to the development of economy and society since 1996,but accumulated reduction of cultivated land for construction has been well correlated to these factors.