As the core of blockchain technology, consensus mechanism affects the security, scalability, transaction processing capabilities and other aspects of the blockchain system. It plays an important role in maintaining the stable operation of the system. This article classifies the existing consensus mechanisms, analyses various typical schemes, gives the basic consensus process, and summarizes the advantages and disadvantages, possible problems, and directions for improvement of various consensus mechanisms. Finally, this article systematically reviews blockchain consensus mechanism and points out some research hotspots and development directions of blockchain consensus mechanism in the hope of providing ideas and reference for the research of the consensus mechanism.