Reservoir construction in high mountain areas usually faces to risks of reservoir leaking, embankment dam fracture, seepage and making internal erosion, landslide in surrounding areas of reservoir. The prevention and repair of these risks need to have suitable investigation methods in order to determine exactly the locations producing these defects. In this paper, the author presents the obtained results from applying a combination of resistivity electrical arrays for searching and determining the spatial distribution of fractures, faults, karsts in the reservoir bed in Chieng Co Village, Son La Province. The investigation results allow us to evaluate the aquiclude ability of the reservoir and to determine the fractured and karstic areas that may cause the water leaking places in the reservoir bed.