The deep environment of strong earthquake preparation in the region of Gansu, Ningxia and Qinghai is analyzed and discussed based on more than two hundred MT measurement data and six artificial seismic sounding profiles, combined with gravitational and geothermal fluid observation data. It is suggested that strong earthquakes often develop and prepare in the top of thick lower resistivity layer, above the lower velocity layer and in the media with dramatic lateral variation electrically and mechanically. The nature of these conditions implies that under the affects of stress, the easiest place for stress concentration is the place where vertical and horizontal deformations of crust layers are inconsistent.