The grounding grid, composed of metal conductors in a mesh structure, effectively addresses overload current issues during lightning strikes and short-circuit faults. The integrity of its structure is crucial for the safe operation of substations. Traditional finite difference numerical simulation algorithms, when calculating the electromagnetic response of grounding grids, are limited by the planar structure of the grounding grid, leading to exceptionally complex grid division and thus limited calculation and identification capabilities. To address this issue, this paper proposes a frequency-domain finite difference algorithm based on multi-grid division technology. By applying multi-grid technology for localized refinement division of the grounding grid, the convergence speed and calculation accuracy of the algorithm are significantly improved. For the problem of boundary computation, a five-point calibration interpolation method is introduced, solving the continuity issue of electromagnetic fields across grids of different sizes. Through algorithm comparison and validation with actual cases, the frequency-domain finite difference algorithm based on multi-grid division technology effectively enhances calculation precision and identification capabilities, especially offering advantages for bodies with more complex structures.