Abstract: Disclosed are a RISC-V and O-CFI mechanism-based defense method and apparatus for code reuse attacks, comprising: constructing a control flow graph according to program source codes randomized in a basic block order; on the basis of the control flow graph, obtaining a boundary range of a control flow transfer branch; executing the program source codes, obtaining a target node to which each control flow is to be transferred, and analyzing each target node in combination with the boundary range so as to defend against an abnormal control flow. The present invention can identify an illegal control flow transfer with the assistance of RISC-V security hardware according to the characteristics of a program control flow itself, and effectively handle code reuse attacks, thereby enhancing the security defense capabilities of an RISC-V system.