The transient electromagnetic method, with its unique advantages of non-excavation and little influence by terrain, has been widely used and recognized in the field of non-destructive testing of surface and underground structures, especially in the detection of corrosion defects in grounding networks. In order to further break through the limitations of the current transient electromagnetic detection system in terms of detection efficiency, accuracy and adaptability, this paper proposes a transient electromagnetic detection method based on pulse modulation. Combined with scanning imaging, the corrosion location of the grounding network can be effectively detected and located. A pulse modulation-based defect detection model is established through theoretical derivation. This model quantitatively analyzes the mapping relationship between the peak information of the pulse-modulated signal and apparent resistivity, accompanied by sensitivity analysis and modulation frequency selection analysis. Leveraging transient response signals of the grounding grid computed using COMSOL Multiphysics in conjunction with scan imaging, the imaging results for several typical defect locations within a 3×3 grounding grid are thoroughly analyzed. This analysis demonstrates the effectiveness and feasibility of the proposed method. Experimental validation confirms that this approach provides a novel and more efficient solution for the non-destructive detection of corrosion defects in grounding networks.