At 4:45 on Sept. 12, 1985, 20 days later after Wuqia earthquake(Ms=7.4), a strong aftershock of Ms=6.7 occurred. A violent seismic accelerograph recorded its waves about 4 kilometers to the epicenter which was determined by the seismograph network. The maximum acceleration of its eastwest component is 123.8 gal, which is four times greater than its vertical component. The corresponding period of the acceleration peak value of the response spectrum of this earthquake is longer than those in Heicheng, Tangshan and Songpan. The intensity of the earthquake motion near the epicenter is equal to 7, but its real failure is only 6.