Based on the correlation data of grain production in Mizhi County from 1990 to 2007，the grey correlation analysis is made to analyze grain production with the variation characteristics of the cultivated land，population，and other influencing factors. Results show that the program for the conversion from cropland to forest and grassland is the main reason for the cultivated land decrease. Improvement of unit yield and total grain production is the key factor to protect grain security. Population growth has a great influence on the bearing capacity of cultivated land and put forward a greater challenge to grain security in the area. To increase the grain yield,some suggestions are put forward,such as increasing science and technology input to enhance unit yield,protecting cultivated land,and excavating the potential of cultivated land. The study provides a scientific basis for government policy making.