Embodiments of the invention disclose a block chain technology-based second-hand car transaction method, device and system. The method comprises the following steps of: broadcasting vehicle information to the whole network by a main node, wherein the vehicle information carries unique identification codes of corresponding vehicles; and receiving information, in the network, fed back by the main node, if the sum of TRUE information in all the fed back information achieves a preset value, putting timestamps on the vehicle information, packaging the vehicle information as new information blocks, sending the new information blocks to a slave node in the network, and writing the new information block into a local database. By implementing the method, device and system disclosed by the invention, second-hand card transaction models are built into decentralized products through utilizing a block chain technology, so that the barrier that the information of the contracting parties in asymmetrical is broken, the trust problem in traditional models is thoroughly changed, and healthy transaction is formed.