Abstract: The diverse actuation system (DAS) is a diverse backup system of protection and safety monitoring system (PMS) to perform the functions of reactor trip and engineered safety features actuation systems (ESFAS). In this paper, the probabilistic safety assessment (PSA) technique was used to identify the DAS functions by comparing the core damage frequency caused by initiating events at power internal event. Furthermore, protection parameter signals of DAS to actuate mitigating systems were identified by accident progress analysis. The results show that the protection functions and parameter signals of DAS can be determinated by this method.