China's Grain Expansion Plan and Its Global Maize Market Effects

China's Second Outline of the Action Plan to Increase Grain Production Capacity by 50 Million Metric Tons places strong emphasis on maize yield improvement; however, its implications for domestic food security and global maize markets remain unclear. This study adapted an open‐source multicountry partial equilibrium model, calibrated it to a 2023 base year, and simulated a baseline and three policy‐induced maize yield‐improvement scenarios for 2030. Relative to the baseline, the Action Plan scenarios increase China's maize production by 4.01–12.19 million metric tons, reduce net maize imports from 22.45 million metric tons to 18.51–10.46 million metric tons, and raise the maize self‐sufficiency ratio from 93.17% to 94.37%–96.82%. Lower Chinese import demand reduces the world maize price by 0.93%–2.84% and contracts global maize trade by 1.31%–3.99%. Synchronized climate shock stress tests indicate that climate‐related production volatility can generate much larger price movements than those associated with medium‐term policy effects. The Action Plan can, therefore, strengthen China's maize security and moderately reshape global trade, but it should be complemented by climate adaptation, diversified trade, and transparent stock management.