Abstract: In order to make up for the defect of insufficient positioning ability of electrical detection method in dam disease detections, it is particularly important to study the response law of transient electromagnetic method to detect leakage hazards of earth-rock dams.By constructing a geophysical model of a dam and using the time-domain finite element method for three-dimensional numerical simulation, the diffusion process of transient electromagnetic field and the characteristics of induced electromotive force attenuation curve under different electrical characteristics and burial depths of the leakage zone were compared and analyzed.The acquired abnormal response curve, apparent resistivity curve and apparent resistivity profile were further analyzed.The results showed that transient electromagnetic responded significantly to leakage hazards and we clarified the diffusion law of transient field inside the dam body.The transient electromagnetic response time of the leakage zone was mainly concentrated in the early delay stage.The maximum response amplitude and time of different types of abnormal bodies were different, proving the feasibility of using transient electromagnetic method to detect leakage of earth-rock dams theoretically.The field test further proved that the transient electromagnetic method was accurate in determining the locations of leakage hazards.The research results can provide a reliable technical basis for reservoir hidden danger investigation and controlling.