A combination of geogas prospecting, radon emanation measurement and soil α measurement was employed in search for the concealed fault in Yala River area of Kangding County, Sichuan Province, which is a potential site of hydraulic engineering. Multi-section measurement composed of 4 measuring lines with a distance of 2 km was performed in a survey area 12 km in length along the Yala River. The intervals between adjacent sampling points along every line were about 20 m. 12 kinds of prospecting data, such as concentrations of several rare earth elements and heavy metal elements in geogas, radon emanation concentrations and α intensities in soil were obtained. The results reflect the actual concealed fault in Yala River area, which consists at least of two branch fault, with the width of each branch fault inferred to be about 40~120 m.