The production of grain sorghum in the United States is the largest in the world. However, its domestic demand is not strong, and therefore, more than 50 % of US grain sorghum has been exported. Thus, the demand and supply of US grain sorghum may be affected by its foreign markets. Japan has been the second largest exporter of US grain sorghum from 1991 to 2010, but the demand for Australian grain sorghum has been growing in the Japanese market. For the identification of factors affecting the supply and demand of US grain sorghum, this research developed a partial equilibrium model that covers the markets in Mexico, the US, and Japan. Furthermore, we investigated how changes in Japanese demand for feeding grain and Australian poultry production affect the demand and supply of US grain sorghum. This investigation tells us that a change in Australian poultry production has little impact on the demand and supply of US grain sorghum. Furthermore, it was found out that the expansion of the demand for feeding grain in Japan may influence the production, price and domestic demand of US grain sorghum initially, but has no effect on these three variables in the end.