After the mainshock occurred in moderately strong earthquake sequence, a large number of earthquakes are likely to be missed due to the far distance from the epicenter, the interference of the coda wave and the overlap of the waveform in the short time, but the integrity of seismic catalog directly affects the scientific and reliability analysis of post earthquake trend determination and aftershock sequence characteristic analysis. In this paper, we adopt a matched filter technique based GPU parallel computing method to detect the missing seismic events in the period from August 1, 2017 to August 12, and obtained 4854 detected events by using 1033 events with high signal-to-noise ratio listed in the seismic network catalog as templates. The number of earthquakes detected was 3.3 times as much as that of the network catalog. In addition to the correction of the single earthquake event in the network, 1797 missing earthquake events were detected, and the complete magnitude was reduced from 1.6 to 1.4. Based on the complete earthquake catalog supplemented with missing earthquakes, we analyzed the activity characteristics of the M_S7.0 earthquake sequence on August 8, 2017 in Jiuzhaigou, Sichuan. The results show that:the foreshock sequence had intensive seismicity enhancement, in a short period of time before the mainshock, and the b-value also showed a low value state, which may be the result of accelerated creep before the rupture of a deep fault. As time went by, the complete magnitude of the aftershock sequence decreased gradually and tended to be stable, and the b-value had a slowly rising trend, so the aftershock sequence would remain in a state of sustained decay in the long term.