Abstract: There is mutual inductance in grounding measurement leads, which seriously affects the accuracy of grounding impedance measurement of large-scale grounding system. Firstly, the mutual inductance theoretical model of ground connection measurement is derived, and the model is solved based on the complex image fitting of the modified term of the mutual inductance. The comparison with the corrected penetration depth formula shows that the complex image method is more accurate for mutual inductance. The mutual inductance numerical laws of 5 D-0.618 method, 2 D-30 degree angle method, 90 degree angle method and reverse method under different lead length and soil resistivity are studied. The results show that 5 D-0.618 method and 2 D-30 degree angle method need to correct mutual inductance, which is caused by mutual inductance in impedance measurement of large-scale grounding system, and negative mutual inductance in reverse wiring method, the degree of mutual inductance should be evaluated in combination with engineering practice.