Depending on mountains and rivers,the Mountain Defense System had been functioning well to an extreme extent in Diaoyucheng,Hechuan,Chongqing,during its 40-year history of defending Mongolia' invasion by turning the single layer defense to a multi-layer one,thus added one of the missions impossible in the world war record.This paper launches a pilot research on how to cope with dangerous mountain top site conditions to defend invading attack with the help of those charming left sites of once besieged city.Those left sites are quite valuable in understanding the history and culture related.