The present invention discloses an identity authentication method based on a block chain network, a server and a terminal device. The objective of the invention is to perform identity authentication of nodes in the block chain network. The method comprises: receiving a registration request carrying user names sent by nodes; obtaining a first block chain account address associated with the user names according to the corresponding relation between the stored user names in advance and the first block chain account address; sending a transaction request carrying the first block chain account address and assigned second block chain account address in advance to the node to allow the nodes to construct a first transaction according to the transaction request and send the first transaction information to the block chain network after the first transaction is constructed, wherein the transaction request shows the operation of performing payment from the first block chain account address to the second block chain account address; determining whether the block chain has the first transaction information of performing payment from the first block chain account address to the second block chain account address or not; and if block chain has the first transaction information of performing payment from the first block chain account address to the second block chain account address, confirming the successful user identity authentication to improve the safety of the authentication.