Abstract: The goal of full awareness of the power grid’s state implies the widespread application of internet of things（IoT） technology in the power grid, where a large number of IoT terminals will be connected to the network through sensing, communication, and computer technologies. Power IoT terminals are characterized by a large quantity, wide geographical distribution, and complex data collection, making them susceptible to breaches and intrusions by attackers. Additionally, traditional centralized authentication systems suffer from issues like single-point failure and performance bottlenecks. This paper, based on blockchain technology, develops and applies technologies such as decentralized identifiers（DID） digital identity based on terminal identifiers, a blockchain-adaptive DID resolver, zero-knowledge proofs based on terminal credential information, and device management based on machine learning algorithms. These technologies culminate in the design of a blockchain-based security authentication system for power Internet of Things terminals. The system has been successfully applied in the power grid, achieving decentralized authentication of IoT devices, reducing network security risks associated with device access, lowering the costs of centralized infrastructure construction and maintenance, and enhancing the efficiency of operations and maintenance personnel.