To further increase the accuracy of fault diagnosis of substation grounding grids, a 35kV substation is studied to measure the surface potential and magnetic induction intensity under normal condition and typical faults, where the fault of corrosion, broken and incomplete weld are simulated. The test results have shown that, the surface potential and magnetic induction intensity of grounding grid are changed differently under different fault circumstances. According to the comprehensive analysis of the variations of surface potential and magnetic induction intensity, the fault and its type can be identified accurately. For the hybrid fault in grounding grid, the variations of surface potential and magnetic induction intensity are similar to the single fault with larger variation degree. This result may provide important basis for future substation grounding grid fault diagnosis.