Abstract: With the goal of "Peak Emission and Carbon Neutrality" and building new power system with renewable energy as main body, energy technology and digital technology are further integrated, and the power grid is accelerating its evolution towards the energy internet. The construction of the energy internet and its digital twin system has put forward higher requirements for the IoT technology, and greatly expanded the connotation and extension of the IoT. This paper focused on how to build a power IoT for the digital twin system of energy internet, analyzed two major scientific problems: physical-digital fusion modelling and collaborative interaction of grid resources, proposed a power IoT architecture and security defense mechanism, and investigated the key support technologies at multiple levels. The key supporting technologies were studied, including accurate sensing and efficient communication, high concurrent access and massive data management, fusion modelling and evolutionary convergence, etc. Finally, the typical applications of power business intelligence supported by power IoT were prospected from three aspects: equipment, grid and users.