An earthquake detection system includes an earthquake data receiving module, for receiving a plurality of earthquake data and generating an earthquake parameter according to the plurality of earthquake data; a threshold value setting module, for setting an earthquake threshold according to the earthquake parameter; and an earthquake detector, for determining whether a new earthquake data belongs to an earthquake event according to the earthquake threshold when the new earthquake data is received, in order to generate a determination result; wherein the threshold value setting module further adjusts the earthquake threshold according to the determination result.