In this article，we have inverted local broadband waveform data to determine the foca1 mechanism of 2011 Anqing MS4. 8 earthquake． Our result shows that the best double couple solution of the MS4. 8 event is 16°，74° and 120° for strike，dip and rake angles respectively． The other nodal plane is 131°，33°，30°;the estimated focal depth is about 3km． The both strikes of the two nodal plane are significantly different with the strike of the Susong-Zongyang fault，which has a low level of seismic activity since Late Quaternary． This implies that this earthquake may not occur on the Susong-Zongyang fault，and we infer that a buried fault with strike of NNE may be the seismogenic structure of this event．