Integrated geologic,seismic sounding,gravity and magnetic field and paleomagnetic studies show that the Alxa Dunhuang landmass is a rigid block with a complete,unified Precambrian crystalline basement.Bordered by Ruoqiang-Xingxingxia fault on the west and Helan Mountain on the east,and wedging itself beneath Qinghai-Tibet plateau on the south and Xingmeng Paleozoic fold system on the north,it occupies a rather large area(91°E～106°E,38°N～42°N).Being an important component part of the North China platform,the Alxa-Dunhuang landmass not only hindered the northward transmission of compressive principal stress of the Indian plate but also caused the close connection of the Tarim platform with the North China platform to form the greater Chinese platform.