Abstract: In recent years, electrical resistivity imaging is widely used in major hydraulic engineering, such as site engineering geological investigation, selecting the location of the dam foundation and bridge pier, detection of mined-out area and ground fissure, many engineering survey areas and so on. Electrical resistivity imaging is applied to detecting geological structure in this article, such as thickness of covering layer of the reservoir dam site area and concealed faults,then, ideal results were obtained on the basis of comprehensive analysis of drilling data and regional geologic data. Finding out the concealed faults and thickness of covering layer in the reservoir area provides important geophysical basis for the determination of reservoir dam site.