As a pivotal infrastructure for building the Internet of Value in the future，consortium blockchain is becoming the frontier of technological innovation. At present，due to the insufficient interoperability between different consortium blockchain applications，credible data and value cannot be exchanged effectively. In order to solve the problem of “data island” and achieve interconnectivity between different consortium blockchain applications，cross chain is considered as one of the most promising and the most anticipated technologies. This report analyzes the key challenges of cross chain and reviews its evolution. It refines the four core technologies：general cross chain interface，isomerous chain interconnectivity protocol，trusted transaction mechanism，and multilateral cross chain governance. This report also introduces the structure of cross chain network and envisions its application in judicial evidence retention，individual data authorization，digital asset exchange and IoT cross-platform interoperability. The profound significance and great value of cross chain technology research have been comprehensively expounded in this report. Blockchain has been included in the list of “New Infrastructure” by National Development and Reform Commission. In order to form a standardized technical system，it is urgent to break down the barriers between different platforms and realize joint construction and management. Cross chain will then be the pivotal technology to achieve the interconnectivity of all chains and build a unified information technology infrastructure，thus serving our national digital economy strategy.