A guidance method for the computerized operation support system is being developed to prevent, terminate, or mitigate boiling water reactor (BWR) plant anomalies. The emergency operation guide, which leads the plant to cold shutdown after reactor scram, is provided by the event-oriented method. This method has two major features; an exact identification of initial causes is not required and an effective guide is provided for malfunctions of the plant cooling system. Off-line and on-line simulation for BWR/5 confirms that the method can provide effective guides for the reactor cold shutdown and respond to changes of plant states in real time.