In recent years, the research on digital twin is in the ascendant. As a new paradigm or concept, it shows great potential. However, the connotation and scope of the digital twin concept is still uncertain, especially the digital twin model definition is not clear. According to the pattern category, the digital twin model can be divided into general model and special model, in which the special model is still the focus of current research, and the research content is mainly embodied in the use of digital twin method to model specific projects. It also includes concept for developing specialized models. These specific projects in addition to the traditional manufacturing related to parts measurement and quality control, manufacturing, design and work processes, as well as system management, but also in the field of biomedical applications and applications for petroleum engineering and so on. There are many tools and techniques for developing special models, such as general industrial software, special industrial software, simulation platform and self-developed secondary development tools, etc. The research object of the digital twin general model is not specific to a specific project, but how to represent the controlled elements of the model as a group of common objects and the relationships between these objects. This provides a consistent approach to the management and communication of controlled elements between different environments. The research on the general model was mainly divided into the conceptual research and the model implementation method; the research heat of the two directions is almost the same. Conceptual research ranges from product lifecycle management to system behavior description, such as general system behavior and system reconfiguration, and to product configuration management, to specific workflow, such as design methods, manufacturing systems and manufacturing processes. The research content is relatively divergent, and there is no particularly prominent hot spot. The research of digital twin general model implementation is mainly reflected in the modeling language construction, the model development methods exploration, the specific tools usage, the Meta-model concept implantation and the model algorithm exploration. Digital twin model is one of the core areas of digital twin research. Its future research focuses on how to integrate the external features and intrinsic properties from different digital twin artifacts into a model with interoperability, interactivity and scalability for more efficient realizing the information flow between the physical world and the digital world, thus achieving the universal digital twin application, and then supporting the CPS (Cyber Physical Space) and CPPS (Cyber Physical Production System) construction. To this end, the next problem in the digital twin model needs to be solved first is how to dock the standard reference architecture, such as the RAMI4.0 (Reference Architecture Model Industrial 4.0) proposed by Germany and the IMSA (Intelligent Manufacturing System Architecture) by China, etc. Secondly, the digital twin model needs a unified method to describe and it also need consistent conclusions, in order to standardize the models established by independent development , thus improving the interoperability and scalability of the model. Otherwise, the performance of the model will decrease significantly as the system scales raise. Thirdly, the research on china's digital twin model requires the support of domestic professional industrial software and modeling software, so that the chinese scholars can carry out in-depth research that is more in line with national conditions.