The fracture failure of substation grounding grid buried underground endanger the safety of equipment and person. However, the current fault diagnosis for the grounding grid is still mainly based on regular excavation detection. This method has shortcomings such as blindness and low efficiency, so the nondestructive testing of grounding grids is of important application prospects. Aiming at the under-determined diagnosis equations defect of the electrical network diagnosis method, this paper proposes the method of applying magnetic field inversion to detect the grounding grid. Considering the electromagnetic interference problem of the grounding grid site, a corresponding hardware system device is designed. First, the grounding grid is analyzed, and the feasibility and specific operation of magnetic field inversion method are discussed. Secondly, according to the characteristics of electromagnetic interference in substation grounding network, a magnetic field detection hardware system with anti-electromagnetic interference ability is developed. Finally, the feasibility and accuracy of the method and system are verified through the experiment on the grounding grid model and the field application of the grounding grid in a substation.