An obstacle in current digital design and manufacturing applications is that the information is hardly shared and exchanged among application systems. From the perspective of supporting assembly information integration throughout product design and manufacturing, a unified assembly information model and its modeling scheme are proposed. The modeling scheme includes a top-down modeling approach, a three dimensional framework describing the characteristics of the model, the model definition given in Unified Modeling Language (UML) and a 3D information expression method. A prototype implementation with CATIA CAD system is introduced to illustrate the application of the model in assembly design, design for assembly (DFA) analysis, process planning, assembly simulation and inspection.