At present, the construction of large-scale water conservancy and electric power projects has been basically completed. It has entered the post-hydropower era and is in the project operation period. The leakage and deformation of DAMS and dikes are the core problems affecting their safe operation. In recent years, a lot of application research work has been carried out on the basis of magnetoresistivity method to solve the problem of concentrated seepage of earth-rock embankment. In this paper, a new detection method, magnetic gradient method, is proposed on the basis of previous research. Firstly, the research progress at home and abroad is reviewed, the basic principle of magnetic gradient method is described, and the distribution characteristics and detection feasibility of the magnetic field vector and its gradient in the leakage channel are analyzed by theoretical model. Secondly, the technical equipment and physical test process involved in magnetic gradient method are introduced. Finally, the engineering case proves that the method can be effectively applied to the detection of seepage channels of embankment and rock, and the future research work of this method is prospected.