Based on the digital broad-band seismic records,the microwave fluctuation impending earthquake was identified preliminarily through the repeated comparative study of Wenchuan,Yushu,Qingchuan and other earthquakes. Its characteristics are as follows:(1)Dominant frequency of spectrum focuses on 11-16Hz. The spectrum range is relatively wide and its morphology is comparatively neat.(2)The phenomenon observed 12-14 days before the earthquake may be recorded by a station with the epicenter distance within 50km.(3)Directional feature is found,and the direction of significant changes in activity is consistent with the causative fault,aftershock distribution,and source locations. The phenomenon of microwave fluctuation impending earthquake can be related to events such as pre-slip,micro-vibration,micro-fracturing in source areas or some related tectonic activities such as micro-activities,micro-cracks,propagations of cracks during the imminent phase.