As the grounding of AC and DC equipment and lightning protection equipment, grounding grids play an important role in ensuring the safety of production operation. Measurement results of several plants show that the grounding impedances are all beyond the standard values, and that the inductive component is too big. A comparative analysis between theoretical simulation and measured results of the inductive component of grounding impedance shows that inductive component, which is generally no greater than resistive component, decreases with the increasing distance between current lead and voltage lead, and that excessive inductive component is caused by mutual induction. Based on the above, a method for calculating and eliminating the mutual inductance between the lead wires is brought out, which lays a foundation for reaching the exact grounding impedance.