Grain production is one of the most important income sources for rural households in the gully area of the Loess Plateau. In order to reveal the input-output conditions and stability of main grain crops production in the area,this paper used 10 years data surveyed from 30 rural households in Wangdonggou valley,Changwu County and mainly analyzed the input and output of wheat,maize,and soybean. Results from the cost-benefit analysis showed that soybean had the highest production stability and its variation modulus of output was 14.2%; maize had the second high production stability and its variation modulus of output was 17.2%; and wheat had the lowest production stability and its change in output was comparatively large. From 1999 to 2008,the output value and production cost of the three grain crops were all increased. Maize had the highest profit,followed by soybean and wheat. Finally,according to the results,some suggestions were given,such as increasing investment in science and technology,enhancing government control power in the prices of agricultural production materials,so as to reduce the cost of grain crops,increase farmers' income,promote stable grain production,and insure regional food security.