Agriculture is a key industry for human survival. For any country, food safety and security are important issues that can’t be ignored. In this article, we propose a new dynamic model which includes the agricultural product market, manufactured product market, manufactured product market, monetary market and adjustment formula of official stock for agricultural products. We also investigate the adjustment path of economic variables from flexible regime to regulated regime when the economic faces supply shock. The result shows that the threshold level set up by the government is a determinant factor in the timing of flexible regime collapse. It is also a determinant factor in the amount of food purchased by the government for food security and the degree of flexibility of agricultural prices.