Aiming at the increasingly complex operation and maintenance problems of power system, this paper combines Beidou precise space-time technology with the theory of digital twin system, and puts forward the method of building the operation and maintenance platform of smart grid. By combining Beidou and Internet of Things sensors, this method can obtain real-time information of power system operating state, equipment working condition and equipment parameters, and take these information as input of digital twin system. By interacting with the actual power system, the digital twin system can form a digital twin operation and maintenance platform that can perform state prediction, fault diagnosis, system self-healing and other functions. The research results show that the method proposed in this paper has reference value for improving the operation and maintenance capability of smart grid.