The embodiment of the invention discloses an energy transaction system and method based on a block chain. The energy transaction system comprises an energy Internet and an energy transaction block chain, wherein energy seller nodes are used for making an energy sales plan and publishing the energy sales plan on the energy transaction block chain; the energy transaction block chain is used for broadcasting the energy sales and subscription plan to all nodes, and performing transaction recording and settlement according to the sales and energy consumption conditions of each node; and energy consumer nodes are used for making an energy subscription plan, obtaining an available energy sales plan and subscribing the energy produced by the energy seller node. According to the embodiment of the invention, the distributed decentralization, trust removal, traceability, tampering difficulty, transparency, high reliability of the system and the characteristics of automation, batch execution and parallel processing of the transaction process of the energy transaction platform are realized by utilizing the characteristics of the blockchain, artificial intelligence, the Internet of Things and the intelligent contract, and the wide deployment of the energy transaction platform between nodes is facilitated.