Abstract: In order to deal with the deficiency of conventional vibration alarm method of steam turbine generator unit,more applicable alarm methods are proposed,that is,short period peak-valley difference alarm method,long period mean value change alarm method and dynamic threshold alarm method based on 3 σ criterion.The key points and applicable conditions of the three improved methods are explained.The effectiveness and practicability of the alarm methods are verified by an example of the vibration fault alarm of the unit on site,which provides reference for the vibration alarm of the units.