On November 6，2011，a M5． 6 earthquake occurred in Oklahoma，United States of America，which was the largest earthquake ever recorded in the region over a hundred years． We used CAP method ( CAP，CAPtele，CAPjoint ) to invert focal depth and mechanism of this earthquake，and the result shows that the double-couple solutions of CAPjoint is: 234°，81°，－170° for strike，dip and rake，respectively． The other nodal plane is 143°，81°，－9°． We also applied different models to verify that the CAP inversion result is effective，with 3° deviation in fault plane solution and 0． 5km in focal depth． The result of CAP shows that the centroid depth of this event is 5km，being a shallow earthquake． Based on the scaling law of source parameters， we obtain the 7． 0km width of rupture zone，top to 1． 4km and bottom to 8． 4km，within the range of water-injection depth of wells． This implies that the M5． 6 earthquake is related to waterinjection during shale gas exploration．