After Ms8. 0 Wenchuan great earthquake in 2008, we immediately installed digital strong earthquake instruments with same type near Wenxian county town, Gansu province, at mountain top, mountainside and foot of mountain respectively, and acquired 12 strong aftershock records. By analysis it is shown that difference of geography has effect to the peak ground acceleration （PGA） of observition point. The PGA values at top of mountain is 1.5 times or so to the value at foot of mountain which in same geological condition. The advantage frequency at the top of mountain are lower than at the foot of mountain, especially for that with bigger recorded values. Under strong ground motion, the differences of PGA and advantage frequency in same place caused by geography condition are main factor for earthquake damage being more serious at top of mountains. The result hints that the earthquake resistant design for engineering and building on difference geographic condition should be different.