With the development and cross-integration of big data, 5G, artificial intelligence, CPS, cloud computing, and Internet of Things technologies, the world is developing in the direction of digitization and intelligence. Digital twin is to build a multidimensional virtual model based on the physical entity. The sensor installed on the physical entity feeds back the data in real time, combines the previous historical data and artificial intelligence technology, and finally analyzes and presents them with software. Because digital twin technology can be well integrated with and applied in many advanced concepts, such as industry 4.0, aerospace, smart city, and smart medical, it has become a popular research direction and main driving technology in many industries and has great development space in all walks of life. This study firstly expounds on the basic concept of digital twin technology, sorts out the development of digital twin technology, further clarifies the relationship between digital twin technology and CPS technology, and introduces the research status of digital twin technology. Secondly, it introduces the key technologies of the digital twin, namely multidimensional and multi-scale modeling, twin data management, and virtual presentation. Finally, the application and development direction of digital twin technology in smart factory, smart city, twin medical, and aerospace fields are discussed, and the digital twin application cases of the original stable heating furnace equipment conducted in the smart factory field by the research team in this study are introduced from the perspectives of scheme, characteristics, and key technologies.