The invention provides an impact grounding impedance measuring system which comprises a high-voltage direct current source, a high-voltage pulse capacitor, a discharging loop, a high-voltage charging switch, a high-voltage discharging switch, a resistance current divider, a water resistance voltage divider, a high-voltage pulse source control table, a digital oscilloscope and an optical fiber signal transmitting system, wherein the resistance current divider is connected with the high-voltage pulse capacitor and the discharging loop in series; the water resistance voltage divider is connected with a reference grounding electrode of the discharging loop; the optical fiber signal transmitting system comprises an optical transmitter, an optical fiber and an optical receiver; the voltage divider and the current divider are respectively connected with the digital oscilloscope through the optical fiber signal transmitting system; and the high-voltage discharging switch is a motion ball gap switch. The invention has the advantages of compact structure, small volume, convenient carrying, simple operation, accurate and stable measuring value, reduction of electromagnetic interference and reduction of measuring error.