Abstract: Food security serves as the cornerstone of national security, and financial support for agriculture is one of the crucial means to safeguard it. Investigating the impact of financial support for agriculture on grain ecological efficiency is of great significance for ensuring national food security, promoting sustainable agricultural development, and optimizing existing financial policies aimed at agriculture. Using provincial-level panel data from China spanning 2012−2021, this study empirically analyzes the influence of financial support intensity and scale on grain ecological efficiency from the perspectives of both absolute and relative financial support levels. The findings reveal that: 1) Financial support for agriculture has a dual impact on grain ecological efficiency, where the intensity of financial support for agriculture significantly promotes grain ecological efficiency, while the scale of financial support for agriculture significantly inhibits it; 2) The positive impact of the intensity of financial support for agriculture on grain ecological efficiency exhibits regional heterogeneity, with the balanced production-consumption region showing the greatest effect, followed by the major producing region and then the major consuming region. The scale of financial support for agriculture has a negative impact on grain ecological efficiency in different regions, with only the major producing region showing a significant effect; 3) Agricultural science and technology innovation, farmland management scale, and farmers’ income are important channels through which financial support for agriculture enhances grain ecological efficiency. To effectively leverage financial funds in enhancing grain ecological efficiency, it is imperative to intensify ecological subsidies, and optimize financial expenditure structures. Differentiated financial policies tailored to various grain functional zones should be implemented. Furthermore, enhancing agricultural technological innovation capabilities, increasing farmers’ income, and guiding moderate-scale farmland management can create favorable conditions for enhancing grain ecological efficiency. Theoretically, by combining the governance of public finance with resource and environmental constraints, an analytical framework is provided for coordinating economic incentives and ecological objectives, which enriches the research scope of ecological economics. At the practical level, the proposal of relevant measures provides a reference for achieving the dual objectives of food security and ecological security in China under the “dual carbon” goals.