Abstract: In view of marine nuclear power system with complex operating modes, relatively simple engineering safety facility, finite operation safety support measure and vital dependence on operators, an on-line nuclear safety support system was studied and developed based on the logic flow of correctly sensing for parameters of nuclear reactor characteristic state→exact judgment for reactor operation state→intervening and treatment for abnormal state. Based on the application requirement of reactor operator, several technology strategies were integrated,such as modeling, simulation analysis, inference engine model, and artificial neural network, to design the system function framework, which included 6 important function modules,involving optimization of nuclear power plant operation state monitoring and alarm analysis, reconstruction of reactor characteristic parameters, intelligent diagnosis of reactor operation event, safety margin assessment for accident conditions, evaluation for reactor core damage and forecasting for radiation consequence. The system could be deployed on nuclear powered vessels independently, to provide marine reactor operator with various kinds of information and technology supports.