The invention relates to a grounding network fault diagnosis method based on a transfer function curve. According to a transfer function change between a state when the grounding network is normal and a state when a corrosion or a break-point fault occurs at the inner part, a lightning impulse signal is used as an exciting signal for measuring a current signal under an impulse excitation and obtaining the transfer function curve of the grounding network. Furthermore grounding network fault diagnosis is performed according to the change of the transfer function curve. The grounding network fault diagnosis method comprises the following steps: 1) inputting the lightening impulse voltage signal U from the signal input line of the grounding network; 2) measuring an impulse current output signal I from the output end of the grounding network; 3) performing fast Fourier transform on the two signals for obtaining frequency domain signals F1(U) and F2(I); 4) comparing the frequency domain signals for obtaining the transfer function curve of the grounding network; and 5) performing fault diagnosis on the grounding network according to the change of the transfer function curve. Compared with the prior art, the grounding network fault diagnosis method based on the transfer function curve has advantages of high diagnosis precision, convenient operation, etc.