A co-simulation framework of a P2P power trading platform and a distribution network based on Blockchain technology is designed for the active cooperation between them to promote the application of Blockchain technology to power trading, protecting fair energy trading. According to the decentralization, strong security, and traceability of the Blockchain, a distributed double auction mechanism is proposed, which is combined with smart contracts to build an energy trading model for simulation analysis. Finally, the distribution network parameters under two scenarios are compared based with the established co-simulation model. Conclusions are drawn on the influence of the P2P power trading mechanism on the distribution network, providing a theoretical basis and a technical support for efficient energy utilization, safe and stable power trading and the application of block chain technology to power trading.