With the rapid development of 3D CAD technology, 3D assembly process is playing an important role in the on-site assembly. A closed-loop control method and three-dimensional site visualization technology site is presented. The methodology takes into account CAD design stage, assembly process design, site assembly and site inspection. The method includes three key technologies: the verification process technology of three-dimensional assembly process, optimization and process simulation techniques of site assembly, closed-loop control technology of assembly process quality inspection. Finally, the method and technology has applied in the actual assembly, and achieved good results.