Based on the weekly data of domestic and international corn prices from January 1,2005 to June 30,2021,we mainly study the relationship between import scale and international grain price transmission as well as the impact of government intervention. Time series models are adopted to investigate the different transmission effects of international corn price on domestic markets under different import scales and the impact of policy intervention on the transmission effect. The results show that transmission effect of international corn prices on domestic marketunder small import scale is stronger than that under large import scale at both mean and volatility levels. Further empirical tests show that the implementation of the temporary purchase policy significantly reduces the impact of international corn price on domestic corn price. After implementing the policy of market acquisition and subsidy,the impact of international corn price on domestic corn price is still weak because China’s corn import accounts for a relatively low share of total domestic supply and the domestic corn price is mainly affected by domestic supply and demand. As the grain import scale continues to expand and the reform of domestic grain market pricing deepens,China should establish the risk prevention and control system for grain markets so as to avoid the impact of drastic international fluctuations on China’s grain markets.