Abstract: This paper adopted double difference earthquake location algorithm to relocate the earthquakes with M_L≥1.0 of the M_S6.0 Yao'an earthquake sequence in 2009 from July 9 to December 23, 2009, and obtained precise locations of 643 earthquakes, and then the focal mechanisms of 20 earthquakes with M_L≥3.0 were determined by using the first motion of P-wave and amplitude ratio method. The stress field of M_S6.0 Yao'an earthquake sequence are obtained by using moving fitting method. The results show that: ① The seismogenic fault of M_S6.0 Yao'an earthquake sequence in 2009 is of right-lateral strike-slip type with NW trending, NE dipping, and high-angle. ② The extend-ing direction of M_S6.0 Yao'an earthquake sequence in 2009 is consistent with that of the M_S6.5 Yao'an earthquake sequence in 2000, so does the focal mechanism solution of mainshock. Both of the two sequences occurred on Maweiqing fault, and the sequence in 2009 occurred on the NE-trending extending of Maweiqing fault. ③ The stress field of M_S6.0 Yao'an earthquake sequence in 2009 trends in NNW-SSE direction, which is coincident with the regional stress field. ④ With the strengthening of regional stress field, the stress accumulation in the source region located at the higher velocity side of transitional zone alternating between high and low velocity zones makes the Maweiqing fault extend NE-wards, resulting in the occurrence of Yao'an earthquake sequence in 2009.