Blockchain is a distributed ledger, which includes public blockchains, private blockchains, and consortium blockchains. How to realize the exchange and transfer of value between different blockchains is an important research topic for the expansion of blockchain technology. This article describes what is cross-chain and elaborates the principles and cases of multi-signature wallet. Then it focuses on analyzing the current significant cross-chain technology and successful cross-chain projects. Finally, this article explores a new cross-chain solution.