Abstract: Based on digital seismic waveform data from Shanxi seismic network, using the P wave first motion polarity and S/P amplitude ratio (HASH) method, we calculated the focal mechanism of ML2.0 earthquakes occurred from 2008 October to 2013 April in the north-central Shanxi seismic belt. The results show that the focal mechanisms of small and medium earthquakes in north-central Shanxi seismic belt are disorder in type and distribution. Besides strike-slip type, there is certain number of normal and thrust types. It indicates that the occurrence of small earthquakes is random and the control of tectonic stress field of North China to the small earthquake in the study area is weak, while local active faults have certain control to small earthquakes.