Abstract: In this paper distributions and lateral changes of five kinds of conductive layers in the crust and upper mantle of Northwestern China are studied; their properties, origins and relations to earthquakes are discussed. Taking the northern portion of the North-South Seismic Belt of China as an example, the deep electrical indexes for delineating the contours of the seismic belt are discussed, and their roles in earthquake activity explained. Analysing some problems of the deep physical circumstance relative to earthquake activity, revealed by the conductivity distributions in the crust and upper mantle, the ability of various deep electrical parameters, as indexes for earthquake risk zoning is discussed; and a method for delineating regions of seismic risk using the above mentioned indexes is given.