The rock and soil body composition of the dam abutment is complex， and the structures are quite different. Under the action of hydrodynamic and hydrostatic pressure， the safety problem of multiple leakage in the joint area， the seepage investigation of a reservoir dam is taken as the research object， the spatial location information and causes of dam hidden dangers are explored by means of measurement， geophysical exploration，drilling and hydrogeological test. The survey results show that the UAV photography technology clearly shows the location relationship between the leakage point， the collapse area and the landslide body， so as to guide the geophysical prospecting work. The focus is the left dam section of the dam. Parallel electrical method technology has the ability to quickly obtain the resistivity distribution of the whole dam. Combined with transient electromagnetic technology， the location and area of the verification borehole can be further determined. Drilling in the section of the pile number K0-000-0+040 m reveal that the dam foundation is mainly composed of block stones， and the electrical conductivity relationship between drilling， collapse area and leakage point water is established through tracer test. It is deduced that leakage is caused by the failure of the inclined wall impervious body in front of the original landslide and the formation of the dam leakage channel in the block stone layer. According to the detection research results， the path and distribution range of the dam leakage channel are determined， which provides a target area for the directional seepage control of the reservoir dam leakage.