Large-scale, complex products are designed collaboratively by different global manufacturers. This leads to problems of deciding manufacturing tolerance of production’s quality in the final assembly process. A new virtual assembly model, called VAFM (Virtual Assembly Fat Model), is presented in the paper. It integrates not only nominal CAD geometry, but also non-geometry information (geometric dimensions and tolerances (GD&T), bill of materials (BOM), process specifications, assembly deform and inspection data). All information of the model will evolve, mature and derived gradually from “thin” to “fat” during the whole cooperative assembly process. The paper presents the definition of a VAFM, its framework and the evolution rules of the fat model. The paper also presents a modeling language based on XML and its visualization. Finally, a case showing the evolution of the VAFM in the assembly process is illustrated.