Abstract: The North China Plain is an important high-yield area of ​​double-cropping grain in my country, and it is also facing huge water resource pressure and ecological environment pressure. This study takes the Ziyahe Plain, a typical over-exploited area and high-yield area in the North China Plain, as an example, and conducts regional "water-nitrogen-grain" coupling simulation based on the SWAT model. The model is calibrated and verified using the measured values ​​of the "water-nitrogen-grain" elements, and the regional farmland water and nitrogen cycle and grain yield in the past 40 years are simulated. The results show that: 1) The model can well simulate the regional "water-nitrogen-grain" elements. Compared with the measured values, the determination coefficient (R2) of the model-simulated evapotranspiration and leaf area index is greater than 0.69, and the Nash efficiency coefficient (NSE) is greater than 0.68; the mean relative error (MRE) and normalized root-mean-square error (NRMSE) of the simulation results of winter wheat and summer corn yields are less than 0.19. In the past 40 years (1980-2022), the region has produced 533.4 million tons of grain, consumed 95.3 billion m³ of groundwater, and generated 4.9 million tons of nitrogen leaching, with an average nitrogen leaching intensity of 109.6 kg N∙ ha^-1. The research results can provide a scientific basis for regional agricultural production and groundwater quantity and quality management decisions, thus serving the regional food security, water security and ecological environment security strategies.