The grounding network plays an important role in the power system for voltage equalisation and current discharge, however, because it is often buried in the ground, its fault detection becomes very difficult, which brings serious hidden danger to the safe operation of the power system. Therefore, accurate diagnosis of faults in the grounding network is of great significance to the stable operation of the power system. Based on the current research situation at home and abroad, this paper establishes a mathematical model for grounding network corrosion diagnosis, and proposes a grounding network fault diagnosis method based on the improved Northern Goshawk Optimisation algorithm. In addition, this paper also takes a 110 kV actual grounding network as an example, and carries out a simulation analysis for the corrosion of grounding network branches. The results show that the improved Northern Goshawk Optimisation algorithm can accurately identify the location of faults, providing a theoretical basis for the development of power system fault diagnosis.