The blockchain is a chain composed of many blocks, each of which is connected in chronological order. Blockchain was proposed by Nakamoto in 2008. Due to the characteristics of decentralization, anonymity and the vigorous development of Bitcoin, blockchain has developed rapidly and has been applied in various industries, including finance, Internet of Things and other fields. However, with the development of blockchain, its own security problems have gradually emerged, allowing attackers to take advantage of various attacks, which has attracted wide attention from researchers in various fields. Many security issues have arisen since the advent of blockchain. Consensus is one of the means to realize the decentralization of blockchain, so the security of consensus layer is one of the most important security problems of blockchain. In order to better solve the security problem of block-chain consensus, this paper summarizes the security problem of blockchain consensus layer on the basis of previous research. In this paper, firstly, we introduce the basic principle of blockchain, next analyzes the security risks existing in the consensus level of blockchain, then proposes the progress and prospect of the blockchain, and finally summarizes the full text.