Abstract: Resonance is a general phenomenon as well as in earthquakes. When a large shock bursts its wave will cause resonance of an earthquake source being pregnant with a shock at later stage. Energy absorbed from earthquake wave is not so much, but the wave can be a sign of earthquake pregnanting progress. That is an alarm signal. The large shock sending signals is called alarm earthquake. The earthquake wave are anisotropy, and the earthquake belt, latitude and longitude are superior in intensities to other directions. There were pre alarm earthquakes in some big earthquakes that damaged cities, such as the earthquake of magnitude 7 8 in Tangshan,the earthquake of magnitude 8 5 in Haiyuan and the earthquake of magnitude 8 2 in Japan Guandong. The pre alarm earthquakes can play an important part in quakeproof in the regions where big earthquakes maybe take place.