Integrated land-sea planning, synergistic mountain-sea interactions, and coordinated development are essential for achieving unified planning regulations, intensive land use, environmental protection, and promoting sustainable socioeconomic development. This study identified eight influencing factors for maritime areas, namely, water depth, slope, sediment environmental quality, ancient river or lake area, sand wave area, sand ridge area, soft soil area, and soft soil thickness, and five influencing factors for terrestrial areas, namely, slope, aspect, terrain relief, distance from faults, and areas prone to geological disasters. By employing K-means clustering, the analytic hierarchy process (AHP), the entropy weight method, and the natural breaks method, an integrated land-sea suitability analysis model was established. The model categorized the Yazhou Bay research area in Sanya into five suitability levels: excellent, good, moderate, poor, and very poor. The geological environmental characteristics of each zone were summarized, and priority planning and development were recommended for areas with excellent suitability, followed by those with good suitability. The results indicate that selecting different influencing factors for land and sea areas but applying the same evaluation method can effectively integrate the spatial planning suitability of both. This demonstrates the rationality and operability of the analysis and evaluation approach. The outcomes serve as a basis for integrated land-sea planning and offer new insights and methods for future planning efforts, providing valuable references.