Abstract: In this paper, a combined method for determining the duration of ground motion is constructed by using the method of earthquake triggering detection and the method of determining the duration of ground motion in seismic engineering. Firstly, the STA / LTA method is used to determine the starting position of the earthquake event waveform. Subsequently, the end position of the event waveform is determined by the combination of bracket duration and effective duration. The calculation results of the early warning record data of Tangshan Guye M_S 5.1 earthquake in 2020 show that the method in this paper can obtain reasonable continuous waveform records of events. With this method, the key seismic event data sequence can be quickly and automatically intercepted from a large number of continuous early warning waveform data, which is conducive to the subsequent application of rapid disaster assessment calculation and processing of earthquake early warning waveform data.