In order to recognize the seismic phases of a regional earthquake automatically, the algorithm of increasing waveform variation value and the criterion of no-subsequent-phase are put forward firstly. The former is to describe the waveform variation of a regional earthquake from its waveform variation value, for capturing the sudden variations of amplitude or frequency of seismic wave by using increase of its value.The latter is used to observe the variations of subsequent waveforms after determining the onset. If there are no other phases in the subsequent waveform, the recognition of onset is invalid. Using this criterion, it will not recognize subsequent phases with bigger amplitudes as the onset phase when the amplitude of the onset phase is too small to be recognized clearly. It shows by the example tests that the accuracy of the method meets the need of the prompt report of earthquake. The relevant programs are compiled.