One or more embodiments of this specification provide a blockchain system, and a message transmission method and apparatus. The method includes: receiving a blockchain message from a blockchain node of a plurality of blockchain nodes in a blockchain relay communication network; sending the blockchain message to a relay node in a relay cluster of a plurality of relay clusters; and transmitting the blockchain message to the target blockchain node through the target relay cluster, wherein each blockchain node of the plurality of blockchain nodes is connected to at least one relay cluster of the plurality of relay clusters, and each relay cluster of the plurality of relay clusters comprises a load balancer and at least one relay node connected to the load balancer.