The invention relates to the field of reverse pricing of a buyer, and provides a method and a system for reverse pricing of a buyer based on a block chain. The method comprises the following steps: receiving a buyer element by a first client, generating a buyer contract according to the buyer element, and recording the buyer contract in a block chain, the buyer element comprising a first element and a buyer price, and the first element comprising a to-be-purchased commodity name; receiving a seller element by at least one second client, generating a seller contract according to the seller element, and recording the seller contract in the block chain, the seller element comprising a second element, a seller price, and the second element comprising a to-be-sold commodity name; and judging whether the seller contract read from the block chain conforms to the buyer contract or not by a server, if yes, generating an intelligent contract for concluding a transaction, and recording the intelligent contract in the block chain, and if not, notifying the first client and the second client of a message characterizing the transaction failure. The invention avoids the control right of a centralized system management platform to the transaction between the buyer and the seller.