The smart energy strategy can provide an energy sharing platform that is interconnected, transparent, and mutually beneficial. The digital twin technology can help break technical and market barriers associated with the development of smart energy. However, the digital twin technology is still in its infancy within the smart energy industry and lacks research on its development and application; a systematic research framework has not yet been formed. This study aims to promote the application of digital twin technology to the smart energy industry by summarizing the development experience of the technology in China and abroad and discussing its future development paths. After comparing the definitions and applications of digital twin technology in different fields, the definition of digital twin for smart energy systems is established, and its general architecture, key technologies, and ecological construction are discussed respectively. Moreover, application cases are briefly analyzed. Furthermore, countermeasures are proposed from three aspects: technology development, ecological construction, and policy establishment. This study is hoped to provide a reference for engineering applications of the digital twin technology in the smart energy industry.