Abstract: After more than a decade of in-depth development, blockchain has formed a blockchain network with different characteristics and suitable for different application scenarios. Due to the isolation of blockchain and the high degree of isomerization between chains, the data flow and value transfer between blockchains have become the technical bottlenecks that hinder the widespread application of blockchain technology. The cross-chain technology of blockchain is an important technical means to realize the interconnection of blockchain and improve the interoperability and extensibility of blockchain. In view of the difficulty of cross-chain interaction between blockchains,the development and application of blockchain cross-chain technology are studied. The basic principles of cross-chain are explained, and the technical difficulties faced by cross-chain technology are analyzed. The current situation is emphasized. Finally, we summarized some cross-chain core technologies about the security risks and practical applications, and discussed the current challenges and future development directions of cross-chain technology.