The CIM digital base framework mainly consists of BIM, GIS, and IOT, which assists to collect video, sensor and other data. At present, there are still many technical difficulties in the integration and compatibility of multi-source heterogeneous models, which bring about difficulty in model data fusion, and lead low model loading efficiency and poor rendering performance. In the present actual projects, the 3D digital base model is mostly based on 3D manual models and oblique photography, which is still far from the goal of BIM application throughout the project lifecycle. Starting from the two core issues of data fusion and rendering performance, this paper establishes a data fusion mechanism for data fusion requirements, analyzes the standardized format of CIM model data (.cim), and explores the lightweight technology of BIM model to improve model rendering efficiency while supporting multi-engine loading of a set of models.