Abstract:We select the seismic phase reports of Tangshan region by Hebei digital seismic network from 2008 to 2018 and calculate the wave velocity ratio by multi station-multi earthquake method and single station-multi earthquake method. We then analyze the characteristics of wave velocity ratio change combined with seismic activity. The results show that using the velocity ratio by multi station-multi earthquake method is more stable, but the results by the single station-multi earthquake method show more detail, and low value anomaly appears in varying degrees before ML≥4.5 earthquakes in the Tangshan region. The locations of abnormal stations correspond to earthquakes, to some extent.