Assessing the geological suitability of urban underground space development is crucial for mitigating geological risks. Traditional 2D evaluation methods fail to capture complex vertical variations in underground space, hindering precise planning. This paper presents an innovative 3D-CWC framework, combining a weighted cloud model with three-dimensional geological modeling, to address vertical complexity and uncertainty in geological assessments. The study area, located in the northern part of Kunming’s Second Ring Road, is divided into 22 million 25 m × 25 m × 1 m 3D units for evaluation. The framework uses the improved AHP and CRITIC methods to assign weights to key geological indicators, addressing both subjective and objective uncertainty, and employs a cloud model to determine geological suitability levels. The results are visualized using 3D geological modeling. The key findings include the following: (1) approximately 71% of the area within a −50 m depth range is suitable or more suitable for underground space development; (2) active fractures and groundwater are the main unfavorable factors; and (3) the geological suitability varies significantly with depth, with shallow areas being less suitable due to soft soil and complex hydrogeological conditions. The framework is further applied to assess the geological suitability of Kunming Metro Line 10, providing valuable decision support for infrastructure development. Compared to existing methods, this framework integrates cloud modeling and 3D geological modeling, offering a more comprehensive approach to handling underground space complexity. It is adaptable and holds potential for global applications, supporting urban underground space development in diverse geological conditions.