Using the waveform data from the Digital Seismological Network of Gansu province, adopting CAP method, the focal mechanism of the 5. 4 earthquake which occurred at JinTan-Alashanmeng on May 3, 2012, is obtained. It shows that the character of focus is strike-slip, the fault rupture plan is 78°, azimuth of maximum principal compressive stress, P, is N32°E, and the focal depth is 9 km.