The establishment of major grain-producing areas is a special strategy implemented to ensure the food security. As important bases of China’s grain production， these areas are also major contributors to agricultural greenhouse gas emissions. From the perspective of food security under the new situation，the increasingly prominent ecological security problem has gradually become the bottleneck restricting the sustainable development of agriculture in China. In this paper，the implementation of the policies of major grain-producing areas in 2004 is taken as a natural experiment，and the double difference model is used to empirically test the effect of the policies on the carbon emission，and explore the carbon emission reduction mechanism in the main grain-producing areas.The research findings of this paper are as follows： 1） From the regression results of the benchmark difference model，the policies of the main grain-producing areas have a significant emission reduction effect on agricultural carbon emissions. In other words，the main grain producing-areas have basically realized the policy objective of “increasing production without aggravating pollution”.2） From the regression results of agricultural carbon intensity，the policy of major grain-producing areas has significantly reduced the agricultural carbon emission intensity in these areas and the three major basins，with the largest reduction effect observed in the Yangtze River basin.3） The mechanism analysis results of policy effects show that the expansion of land management scale is an important mechanism to produce emission reduction effects. Therefore，it is recommended to promote the scale of planting and aquaculture， develop appropriate scale operation，further optimize the agricultural industrial structure，and increase the proportion of low-carbon industries，so as to achieve the goal of coordinated development of grain production and ecological environment.