China has recently implemented a policy to promote potato as a national staple food and to close its large yield gaps with other countries. The carbon–land–water implications of this policy are examined here by compiling and analysing detailed city-level life-cycle inventories of China’s staple crops. We find that in general potato, despite relatively low yields, has lower greenhouse gas emissions and water demand than other staple crops (maize, wheat and rice) on a per-calorie basis, but substantial regional variation exists for each crop. Integrating potato as a staple in China to meet increases in food demand and close the yield gap has the potential to reduce the total carbon–land–water impacts of staple crops by 17–25% by 2030. However, an unsuccessful integration runs the risk of global burden-shifting if the policy, for example, reduced domestic rice production and led to increased rice imports. Potential synergies between food security and environmental sustainability in China can be created by the potato policy, but greater efforts are needed to promote potato across the entire food supply chain from production to consumption.