The Yao'an,Yunnan M_S6.0 earthquake occurred at 19:19 of July 9,2009. At 17:02 of July 10 and 00:01 of July 13,the M_S5.2 and M_S4.7 earthquakes occurred. We applied the Cut-And-Paste(CAP)method to determine the focal mechanism,and found the earthquake is a strike-slip event,with two nodal planes striking 203 degrees and 295 degrees. Active faults have not been found in previous regional geological survey,so it is difficult to determine the seismogenic fault. We use the relative centroid location method to determine the earthquake's rupture directivity,and found that the nodal plane with the strike of 295° is the ruptured plane. We also investigated the result's robustness against the error of location,original time and focal mechanism,and found the resolved rupture directivity is stable.