In this paper, using seismic data recorded by the active source network of the Qilian Mountain and the digital seismic network of the Gansu Province, we relocated the Zhangye M5.0 earthquake in 2019 and its aftershock using the double-difference location and genetic algorithms. Relocation results of 30 seismic events were also obtained. These results indicated that the main position of the earthquake was 38.502°N, 100.254°E, and the focal depth was 14.7 km. The aftershocks were relatively concentrated and distributed along the Changma-Ebo fault. The source depth was mainly distributed in a range of 5-15 km, while the aftershock sequence was distributed along the SW-NE.