Abstract: Addressing the challenge of widely diverse data sources for BIM models, current model visualization faces limitations such as client software dependencies, data redundancy, and the lack of interoperability between macro-level Geographic Information Systems (GIS) and micro-level Building Information Modeling (BIM). This paper proposes a novel solution based on the extensibility of the I3S data specification to achieve efficient integration and visualization of multi-source heterogeneous model data. By developing custom B3D data files, multi-source heterogeneous model files are uniformly deconstructed into B3D files and stored on the server. Leveraging the streaming transmission capabilities of the I3S technical standard, seamless integration of multi-source BIM models with real-scene models, point clouds, and GIS maps is realized. The solution supports viewing and operations across multiple terminals, including web browsers and mobile devices. Experimental results demonstrate that the engine platform efficiently handles large-scale 3D data, enabling real-time visualization and interactive operations in complex scenes. This research introduces a new concept and methodology for the integrated application of multi-source heterogeneous data, providing a solid technical foundation for smart city construction and management.