Control-flow hijacking attacks exploit memory corruption vulnerabilities to grab control of the program, and then hijack the program to execute malicious code, which brings a great threat to system security. In order to prevent control-flow hijacking attacks, researchers have presented a series of defense methods. Control-flow integrity is a runtime defense method that prevents illegal transfer of process control-flow to ensure that control-flow is always within the range required by the program. In recent years, more and more research works are devoted to solving related problems of control-flow integrity, such as presenting new control-flow integrity schemes, new control-flow integrity scheme evaluation methods, etc. This study explains the basic principles of control flow integrity, and then classifies existing control flow integrity schemes. The existing evaluation methods and evaluation indicators of the control-flow integrity scheme are introduced at the same time. Finally, the thoughts on potential future work on control-flow integrity is summarized, which, hopefully, will provide an outlook of the research direction in the future.