Under the dual influences of China’s new urbanization strategy and ecological civilization initiatives, balancing land development and ecological security has become a challenge in territorial spatial planning. This study focuses on the central urban area of Jianyang, Nanping City in Fujian Province, a region characterized by typical mountainous terrain. Following the Guidelines for Resource and Environmental Carrying Capacity and Territorial Spatial Development Suitability Evaluation (2020), we established a multi-level decision-making framework that innovatively integrates a multi-tiered terrace classification system with dynamic hydrological process analysis. Through constructing an evaluation system encompassing land resources, water security, ecological baseline, and geological disaster risks, we employed GIS-based spatial overlay analysis, water-soil resource matching matrices, and hierarchical response mechanisms to assess terrain gradient effects and ecosystem service constraints on development decisions. Key findings include: (1) the region exhibits a “core-axis prominence with peripheral differentiation” pattern, where high-capacity zones along Chongyang River benefit from gentle topography, wide valley plains, and abundant runoff; (2) suitable development areas total 142.08 km2 (42.2%), forming a “dual-core with flank expansions” pattern centered on Tancheng-Tongyou urban core, expanding through Jiangkou-Xingtian axes; (3) differential strategies are proposed, prioritizing high-tech industries and eco-tourism in high-capacity zones while enhancing ecological restoration in low-capacity areas. This study innovatively combines terrace classification theory with dual-evaluation frameworks, providing a quantifiable decision-support system for sustainable slope land development in southeastern hilly regions.