To solve the grid-connected dispatch problems of controllable load under the development of distributed power transaction mechanism, a decentralized transaction mode between controllable load users and load agents based on blockchain technology is proposed. By integrating the operation characteristics of controllable load users and fully considering the demand information of electricity purchase and sales between different sub-categories of users and load agents, two types of decision model functions of controllable load users and load agents are designed. Based on the basic principle of best interest, the blockchain node model is established considering operation and maintenance cost and operation efficiency. The simulation analysis of 500,000 residents in a central city on a typical summer day shows that the penetration rate of electric vehicles is 20% and that of air conditioners is 30% by assuming that the electricity price of the load agent selling electricity to the power grid is 0.5 yuan/(kWh), the unit damage cost of the electric vehicle power battery is 0.14 yuan/(kWh), and the agency fee of a single electric vehicle user is 0.1 yuan/d. The analysis results of an example show that the proposed optimal dispatch strategy fully taps the potential of controllable load users and load agents for peak load shifting of power grid, achieves economic optimization for both parties, and guarantees the long-term effective operation of blockchain network, thus providing reference value for the application of blockchain technology in power demand response.