<p>Land use plans are closely associated with landscape changes. Since the 1990s, China has implemented quota-based farmland protection planning to attenuate farmland loss and ensure food security. However, existing literature has primarily focused on compliance with planning blueprints, rather than on the varying impacts of planning on farmland use and underlying mechanisms. To bridge this gap, this study argues that China’s farmland protection planning was implemented as a “soft constraint”, with its impacts moderated by economic forces. This study examined this hypothesis by taking National General Land Use Plan (2006–2020) as a case study. Employing a two-way fixed-effects model, robustness checks and heterogeneity analysis, this study convincingly assessed the plan’s effectiveness by comparing outcomes across prefectures with varying protection targets and different economic driving forces. Results suggest that the planning significantly reduced farmland loss by aligning with economic forces, although farmland area quotas were not fulfilled either nationwide or in most prefectures. Moreover, the planning was more effective in regions with higher benefits and lower opportunity costs of plan implementation, thereby amplifying the spatial shifts of farmland. These findings deepen the understanding of what determines planning effectiveness, helping researchers and policymakers evaluate the implementation and spatial variance of other land use policies.</p>