This specification provides a message transmission methods and apparatuses. One method includes: receiving a digital certificate sent by each blockchain node of a plurality of blockchain nodes in a blockchain relay communication network, wherein the digital certificate comprises identity information of each blockchain node of the plurality of blockchain nodes and a network identifier of a blockchain network of the blockchain relay communication network that comprises a corresponding blockchain node of the plurality of blockchain nodes; verifying that a digital signature of the digital certificate is authentic based on a public key of a certification authority (CA) issuing the digital certificate; and recording a mapping relationship between the identity information of each blockchain node of the plurality of blockchain nodes and the network identifier.