One or more embodiments of this specification provide a method and an apparatus for transmitting messages, being applicable to a relay node in a blockchain relay communication network. The method includes: registering, based on a registration request submitted by each blockchain node, the blockchain node to a blockchain node set indicated by the registration request; determining, when receiving a blockchain message sent for a target blockchain node set, a target blockchain node registered to the target blockchain node set and a target relay node in the blockchain relay communication network and connected to the target blockchain node; and transmitting the blockchain message to the target blockchain node through the target relay node.