Blockchain technology has good performance and prospects in ensuring the information security and privacy of power users, but its decentralized characteristics have brought the problem of excessive node storage pressure, resulting in excessively slow operation of node servers and low transaction processing performance. In order to reduce the storage task of nodes, methods of multi-chain management and cross-chain query are proposed. The multi-channel technology is used to isolate the ledger in multiple channels and realize the multi-chain management of huge data nodes. In response to the problem of "data islands" between multiple chains, intermediary nodes are added and key-value query methods are combined to achieve cross-chain query, thus successfully building a power user information blockchain management system with multi-chain management and cross-chain query. System testing shows that under the premise of ensuring user information security and privacy, the problem of excessive node storage pressure is effectively alleviated, and the system is stable and efficient and can be cross-chain query. This method realizes the safe storage of power user information, efficient system operation, and global data sharing, and provides a reference for promoting the digital construction of the national power grid.