One or more embodiments of this specification provide message transmission methods and apparatuses. A method includes: registering each of a plurality of blockchain nodes in a blockchain relay communication network to a blockchain node set indicated in a registration request submitted by a corresponding blockchain node of the plurality of blockchain nodes; generating a routing policy corresponding to each of the plurality of blockchain nodes, the routing policy comprising a blockchain node set that the corresponding blockchain node belongs and a relay node that connects to the corresponding blockchain node; receiving a blockchain message for a target blockchain node in a target blockchain node set; determining a target relay node connected to the target blockchain node according to a tree-structured routing table obtained by organizing routing policies in a tree structure; and transmitting the blockchain message to the target blockchain node.