Since 2001, small-moderate seismicity has been increasing obviously in Pingliang area, Gansu province. In this paper, the focal depths are definite by the locating method based on genetic algorithm, the focal mechanism is calculated by the moment tensor inversion. According to seismic spatio-temporal distribution, seismic phase and regional geological structural environment, it is considered that the earthquakes in Pingliang area are mainly mining-induced earthquakes, and the kinds of initial mechanism are coal body compression, work face stretching and fault rockburst.