Abstract: Blockchain technology promotes the further development of smart grids through the execution of smart contracts and the secure storage of transaction data. However, due to the uncertainty of user power output and individual profit-seeking characteristics, there are a lot of untrustworthy power transactions in smart grids. The phenomenon of breach of contract leads to problems such as low efficiency and serious waste of resources in the power grid blockchain system. For this reason, a grid power trading mechanism based on smart contracts was designed to constrain the behavior of nodes through credit values. The credit group voting method of grid blockchain node election was proposed through the design of two-factor fair grouping, responsible voting and other methods, which ensured the reliability of blockchain node election. By optimizing the number of participating consensus nodes, it reduced the practical Byzantine fault-tolerant algorithm (PBFT) traffic. The experimental results show that the proposed scheme can efficiently complete the grouping and node election process, prevent malicious nodes from participating in the consensus, reduce communication overhead, and improve the stability and security of the system.