China has implemented a range of demographic policies to address population ageing, which exert significant potential impacts on aggregate food demand and associated environmental effects. However, prior studies have not integrated these policies and age-specific food consumption patterns into environmental impact projections. Here, we quantify China’s four food-related environmental footprints under representative demographic policy scenarios by employing a Quadratic Almost Ideal Demand System (QUAIDS) and a multi-regional input–output (MRIO) model. This study is the first attempt to link China’s pro-natalist policies with multi-dimensional food-related environmental footprints through an age-cohort demand model. We find older adults (> 60 years) will become the largest contributor to the nation’s total food-related footprints (accounting for approximately 37% by 2050), despite having below-average per capita footprints. From 2020 to 2050, total land use footprint is projected to increase, whereas GHG emissions, water consumption, and eutrophication footprints would decline. Reduction in GHG emissions is primarily driven by declining environmental intensities, while changes in other three footprints are mainly due to dynamic population sizes. Relative to the no-policy baseline scenario, China’s demographic policies could lead to an approximate 3–18% increase in environmental footprints by 2050, imposing a notable burden on sustainability targets. Land use footprint would emerge as the most policy-sensitive indicator, with its peak year delayed by at least a decade under the most aggressive fertility-boosting policy. By analyzing dietary change scenarios, we find only ambitious transitions (nationwide adoption of plant-rich diets) can fully offset the policy-induced footprint increases, except for water consumption, in which case plant-rich diets would conversely result in higher footprints. Our findings underscore dietary change can help mitigate the additional environmental pressures induced by China’s demographic policies, while also highlighting critical trade-offs across different environmental indicators.