Security system vulnerability is closely related to the occurrence and development of security accidents in petrochemical plants. It also affects security accident evolution, and the state of security accident changes and in turn acts on the system vulnerability. However, few studies have been performed on the coupling effect of security system vulnerability and security incidents on this evolution process. In this study, the correlation between security system vulnerability and security incident is analyzed from three aspects, namely, evolutionary roots, time dimension, and space dimension. A full-cycle coupling evolution model between security system vulnerability and security incidents is established. The quantitative coupling evolution law among them is also obtained. The coupling evolution relationship between security system vulnerability and security incidents in petrochemical plants is examined in detail, and an illustrative case is used to explain the rationality of our findings. Results reveal that security system vulnerability plays a leading role in each of the four security incident evolution periods.