Abstract: By studying the difficulty of cross-chain communication between blockchains， this paper develops and improves functions based on the relay-based cross-chain communication mechanism， and designs a relay-based alliance chain cross-chain communication system. Through the cross-chain system， cross-chain requirements such as interconnection of heterogeneous chains， addressing and forwarding of cross-chain requirements， cross-chain resource invocation， and cross-chain contract initiation are realized. A two-phase execution protocol for cross-chain communication is proposed， which fully guarantees the atomicity of cross-chain interaction. The block header synchronization contract is designed for cross-chain transaction verification， which simplifies the cross-chain transaction verification process and reduces the complexity of cross-chain communication. Through the functional test of the experimental simulation system， the cross-chain system designed in this paper can safely and efficiently realize the cross-chain communication operation between the blockchains.

Key words: blockchain, cross-chain, relay, block header verification, phase two agreement