Abstract: With the development of nuclear power, the risks of safety and reliability brought by digital control system (DCS) and equipment in nuclear power plant (NPP), have gained widespread concern and attention. The technology of status monitoring for NPP is constrained by paying attention to single equipment, their inter relationships and the influences of reliability intendancy for the whole system were ignored. A status monitoring and reliability predication method was proposed in this paper, and the high pressure safety injection system was taken as an example. By monitoring the status information of several related equipments, and analyzing internal reliability relation, the influence of the current reliability trend of the equipment on the reliability of the whole system was obtained, and the system reliability model was established. The reliability of the whole system can be monitored in real time with this model by updating the status information, which can provide a comprehensive indication for NPP system and equipment, and also can provide the guidance for the system management, equipment management, operation and maintenance.