Abstract: A M 6.9 earthquake of 1981 occurred in the Daofu region in western Sichuan Province,an epicetre being siruated about 2km southeast of Daofu with an intensity of 8.On the basis of field investigations,including structural conditions,recent crustal movement and tectonic stress fields of the seismic region alongwith ground fractures,isoseis-mals,ground motions,aftershocks,focal mechanism solutions and geodetic observations,the Authors incline to consider that the event in question is caused by sinistral motion of the Xianshuihe fault under the action of nearly EW-trending tectonic stress field.Also discussed in this paper are locking of the fault and migrating of earthquakes along the northern segment of the fault.