The complexity of car-body welding and assembly process makes it difficult for engineers to design and analyze the process parameters. Therefore, a tree-relation mixed data model, based on the characteristics of car-body assemply process, is put forward to represent the welding and assembly process. By integrating this data model with CAD/CAM model and 3d graphic simulation platform, a visual information model is built up. A case study is performed on the visualization of car-door welding and assembly process plan using this information model. The result shows that the model is able to represent the process plan of welding and assembly process visually and integrally. The model can be used for auto-body design, welding-process analysis and design, process information management, quality control and personalized selling.