A measurement apparatus using impulse current to simulate lightening as the test current to measure grounding impedance is given. While injecting impulse current created by impulse current generator（ICG） into grounding systems， the data acquisition device collects the voltage and current signals of grounding systems respectively， which are then converted by A/D device and transformed by fast Fourier transform（FFT） into frequency domain. Through the spectrum calculation method， the impulse grounding impedance can be obtained and further divided into resistance and inductance component. Lab and field tests are performed by comparing with the magneto ohmmeter method and the effectiveness of the method proposed is verified by EMTP simulation results.