Abstract: Aiming to find out abnormal changes of important devices in nuclear power plant operation process, combined with data mining technology, dynamic regular library of important devices was set up. Based on the real-time data and the history data of real-time information monitoring system in nuclear power plant, trend and regularity of important devices of nuclear power plant were obtained and analyzed, so the important devices can be monitored and pre-warn online. The basis can be provided for the operators, so the probability of nuclear accidents would be reduced and the safety of operation for nuclear power plant can be effectively improved.