Conventional alarm system has many difficulties in the operator``s identifying the plant status during special situations such as design basis accidents. To solve the shortcomings, an on-line alarm annunciator system, called Dynamic Alarm Console (DAC), was developed. In the DAC, a signal is generated as alarm by the use of an adaptive setpoint check strategy based on operating mode, and time delay technique is used not to generate nuisance alarms. After alarm generation, if activated alarm is a level precursor alarm or a consequential alarm, it would be suppressed, and the residual alarms go through dynamic prioritization which provides the alarms with pertinent priorities to the current operating mode. Dynamic prioritization is achieved by going through the system-and mode-oriented prioritization. The DAC has the alarm hierarchical structure based on the physical and functional importance of alarms. Therefore the operator can perceive alarm impacts on the safety or performance of the plant with the alarm propagation from equipment level to plant functional level. In order to provide the operator with the most possible cause of the event and quick cognition of the plant status even without recognizing the individual alarms, Reactor Trip Status Tree (RTST) was developed. The DAC and the RTST have been simulated with on-line data obtained from the full-scope simulator for several abnormal cases. The results indicated that the system can provide the operator with useful and compact information for the earlier termination and mitigation of an abnormal state.