A blockchain-based transaction system for a green certificate includes an audit node, a proxy node, and an off-chain node. The proxy node is used by a power producer and a purchaser; the audit node verifies qualification information of the power producer, and send a green certificate to the power producer; the off-chain node predicts a transaction price of a next transaction; when receiving sale information of the power producer and purchase information of the purchaser, the proxy node sends the sale information, a digital signature of the power producer, the purchase information, and a digital signature of the purchaser to the off-chain node; the off-chain node matches the sale information and the purchase information, and sends successfully matched transaction information to the proxy node; the proxy node sends the successfully matched transaction information to a transaction smart contract; and the transaction smart contract performs transaction processing.