A modeling method based on building information modeling (BIM) + geographic information system (GIS) + oblique photography technology was proposed to address the issues of low efficiency and difficulty in data fusion in integrated 3D modeling of mountain tunnels above and below ground. Taking the Huanglongshan Tunnel in Wuhan as an example, firstly, the mountain tunnel components were classified according to their purpose and construction process. Using Revit and Dynamo software, a three-dimensional structural model of the tunnel was constructed using parametric modeling and adaptive splicing methods. Secondly, surface images were obtained through drones, and a 3D realistic model was constructed using oblique photography technology. By using image matching and filtering techniques to process point cloud data, a digital elevation model (DEM) was generated, and combined with borehole data, a three-dimensional geological model was constructed using interpolation and constrained partitioning methods. Finally, based on MapGIS, the integration of tunnel structure model, surface 3D realistic model, and 3D geological model was achieved. The proposed method can optimize model management, reduce data loss, and achieve integration and sharing of tunnel engineering information.