On the basis of expounding the connotation of basic terms such as system, model, architecture and model architecture, this paper discusses the relationship between problem architecture, design activity architecture and system architecture. By means of the problem structure, a complete model system and a perfect model architecture are put forward to provide beneficial support for system design. The problem this paper explores is to reveal the possible reason affecting system engineering practice. It is hoped that the development of the model system will be paid more attention to in practice, so as to avoid losing integrity when using the model. Integrity is just one of the key points of systems engineering.