Using the focal mechanism solutions of aftershock sequence of Dayao M6. 2, M6. 1 earthquakes occurred on Jul. 21 and Oct. 16 in 2003, we inversed the tectonic stress of these two strong earthquakes by slips direction fit- ring method and obtained their tectonic stress variation. Basing on the tectonic stress of these two earthquakes, we calculated static coulomb failure stress variation after these two strong earthquakes and studied whether the tectonic stress of Dayao M6. 2 earthquake triggered the Dayao M6. 1 earthquake. The results showed that the maximum principal stress S1 of tectonic stress field which was nearly horizontal action with NE turned to NEE di- rection in the focal zone after two strong earthquakes. The Dayao M6.2 earthquake on Jul. 21 apparently trig- gered the Dayao M6. 1 earthquake on Oct. 16 in 2003.