Abstract: In order to solve the problem of low degree of automation in the application layer network protocol fuzz testing, an application layer protocol fuzzy testing based on network protocol reverse engineering technology is proposed. In this paper, the LCS algorithm and the multi-sequence alignment algorithm are used to analyze the characteristics of the application layer network protocol, and the protocol format of the fuzz testing is automatically constructed. The required test cases are generated according to the protocol format. The experimental results show that the scheme reduces the dependence on the specification of the manual analysis protocol, and the result of the protocol analysis can effectively exploit the protocol loopholes and have some reliability.