Abstract: With the gradual advancement of the sixth-generation mobile communication system (6G), the digital twin technology for wireless channels, as one of the critical technologies for future network evolution, has received widespread attention. This paper summarizes the background, system architecture, critical technologies, and future development direction of the digital twin technology for wireless channels. Firstly, this paper introduces the development background and demand of digital twin technology for wireless channels, as well as its system characteristics and research progress. Then, this paper discusses critical technologies such as multi-medium electromagnetic (EM) parameter acquisition in complex environments, high-performance ray-tracing (RT) simulation technology, and hybrid channel modeling driven by both models and data. Finally, the paper looks forward to the development of wireless channel digital twin technology in the 6G era and summarizes potential standardization work. The digital twin technology for wireless channels provides the ability to model wireless channel characteristics and predict effects for EM wave propagation by constructing a virtual twin of the wireless channel, which is of great significance for developing 6G and future communication systems.