In 2014, the Chinese government launched a comprehensive agricultural water use reform policy (CAWURP) for the conservation of agricultural water. Thus, the question as of as to how the implementation of this policy affects food production has arisen. To answer this question, we use Chinese provincial data from 2004 to 2021 and apply the difference-in-differences (DID) method to explore the relationship between the CAWURP and food production. The results show that the CAWURP can significantly improve food production, which means that water conservation and food production growth can be achieved simultaneously. Moreover, the CAWURP can enhance technological innovation and promote large-scale crop cultivation, which is conducive to enhancing food production. Regional division based on the CAWURP, economic development level, and food production area type significantly impacts the effect of the CAWURP. For example, policy reforms have been more effective at increasing food production capacity in the northeastern and eastern regions. However, such policy reforms have been less effective in the more water-poor northwestern region and in the major food-producing regions. Based on these conclusions, this study suggests that the Chinese government should differentially implement the CAWURP by, for example, strengthening the level of policy implementation in Northwest China and adjusting policy implementation projects in not only the major food-producing regions of the country but also Central China to enhance the effectiveness of policy implementation. This study provides a useful reference for other countries aiming to conduct agricultural water reforms and enhance food security.