Abstract: The evaluation of the operation condition of power transmission and transformation equipment is an important means to ensure the safe and stable operation of power system. The traditional state evaluation of power transmission and transformation equipment has bottlenecks such as incomplete state perception, low data quality, and difficulty in building evaluation model. Digital twin technology opens up the whole link process of entity-perception-modeling-application. Based on the new sensing technology, the comprehensive perception of the condition of power transmission and transformation equipment is realized. According to the operating characteristics of power transmission and transformation equipment, sensor device evaluation, and data in-depth governance are realized. Based on big data analysis, data mining and other technologies, the digital twin of power transmission and transformation equipment is constructed, which realizes the state differentiation evaluation, accurate fault diagnosis and accurate state prediction of power transmission and transformation equipment. The in-depth integration of digital twin and condition assessment technology will promote the operation and maintenance management of power transmission and transformation equipment to a smart era. This paper analyzes the application of digital twin technology in the condition assessment of power transmission and transformation equipment, and elaborates the specific application of digital twin technology including condition sensing, data governance, model construction, and application. The application status of digital twin technology in the condition assessment of power transmission and transformation equipment is summarized and discussed, and prospects in its future development trend are presented.