The waveform and observation report data of 107 earthquakes with ML
≥1.5 recorded by Chongqing Digital Seismic Network in Wulong area were selected. The waveform cross-correlation technology was used for correlation calculation. 12 groups of repeating earthquakes with waveform correlation coefficient larger than 0.8 and recorded by 3 seismic stations at the same time were identified. The position of repeating earthquakes in Wulong area was normalized by ray tracing method, and the change of P-wave travel-time difference of the selected stations was obtained. The results show that four years before the 2017 Wulong MS
5.0 earthquake, there are long-term negative abnormal changes in P-wave travel-time difference recorded by Wulong, Xiannushan and Fuling seismic stations, lasting for 339 days, with a total of 18 negative values. It shows that the crustal medium velocity increases obviously in this period.