The invention discloses an impact grounding impedance measurement system and a measurement method. The impact grounding impedance measurement system is mainly composed of a portable small impact current generator, a high-voltage probe, a current sensor and an oscilloscope. Based on a measured p-E curve and an impact grounding impedance value measured under a small impact current, proportionality coefficients with the impact small-current grounding impedance as a benchmark are obtained by simulation software COMSOL under the premise of considering the influence of factors such as soil parameters, current parameters and grounding body size on impact grounding impedance and fully embodying the spark effect and the inductance effect. The proportionality coefficients are multiplied by the grounding impedance measured under a small impact current, and the actual impact grounding impedance of a grounding body is obtained finally through correction. The method is of high accuracy. The problem in the prior art that the simulated experiment or simulation method adopted for measuring the impact grounding impedance of a grounding system has the disadvantages of low accuracy, complicated measurement and high cost is solved.