The geological environment in karst regions is inherently fragile, necessitating a suitability assessment for tunnel planning to mitigate geological issues induced by construction activities. A pressing challenge is to develop a detailed three-dimensional geological model in karst mountainous areas, which can serve as the foundation for conducting a comprehensive 3D suitability evaluation for tunnel planning.This study focuses on the Liangjiang segment of Zhongliang Mountain in Chongqing as the research area. Employing geological modeling methods and grid subdivision techniques tailored to the regional geological characteristics, a series of detailed 3D geological and attribute models have been constructed. Based on the Analytic Hierarchy Process (AHP) and a multi-level index overlay method, a 3D evaluation system for tunnel planning has been established, aligned with the local geological conditions and the current state of tunnel construction. Furthermore, the 3D evaluation results have been utilized for tunnel planning assessment and analytical applications.The findings indicate that by employing appropriate 3D modeling methods, one can construct detailed geological models in karst mountainous regions. This serves as a foundational data source and spatial analysis framework, enabling the establishment of a 3D suitability evaluation system for tunnel planning that is consistent with the local geological environment. The results provide substantial support for the planning and site selection of tunnels in karst mountainous areas and the optimization of underground space patterns in mountainous cities.