Abstract: The Greater Food Approach reflects China’s transition in food security governance from a emphasis on grain quantity toward the coordinated pursuit of a diversified food supply, improved nutrition, and ecological security. This transition places new institutional demands on the “three-in-one” protection of cultivated land in terms of quantity, quality, and ecology. Drawing on the theories of cultivated land multifunctionality and human–land systems, this study develops an analytical framework for “three-in-one” cultivated land protection under the Greater Food Approach. It explains how the quantity, quality, and ecological condition of cultivated land interact to determine its comprehensive capacity to safeguard food security. It also examines three major transformations in cultivated land protection: from emphasizing a single production function to providing comprehensive support, from output-oriented utilization to structural adaptation and differentiated use, and from rigid regulation to governance that combines constraints with incentives. The practical challenges arising from these transformations are also analyzed. The study argues that “three-in-one” cultivated land protection should follow four fundamental principles: coordinating quantity with quality, reconciling agricultural production with ecological protection, balancing government regulation with market mechanisms, and coordinating local and national interests. On this basis, policy efforts should focus on optimizing land-use regulation, improving systems for assessing cultivated land quality and production capacity, strengthen incentive mechanisms, regulating the use of cultivated land for facility agriculture, and expanding opportunities for its multifunctional use. These measures would facilitate a shift from area-based control toward comprehensive functional governance capable of supporting national food security.