The embodiment of the invention discloses a communication method and a service data transmission method in a blockchain network. The block chain network comprises a P2P network and a relay network. The blockchain node in the P2P network sends a detection message to other blockchain nodes through the P2P network and the relay network respectively; and obtaining first service quality data corresponding to the P2P network and second service quality data corresponding to the relay network according to the sending time of the detection message and the receiving time of the response message, and recording link optimization information according to a comparison result of the first service quality data and the second service quality data. Therefore, the block chain node and the relay node can select the network communication link with better service quality to transmit the service data according to the link optimization information.