Abstract: For comprehensive research on formation process of arc grounding over-voltage in mine power supply system, a mine power supply system model and an intermittent arc grounding model were built by use of real time digital simulator, and over-voltages in processes of power frequency arc extinction, high frequency arc extinction and hybrid arc extinction were simulated. The simulation results show that the maximum transient over-voltage under condition of power frequency arc extinction theory is slightly lower than historical measured value; the maximum transient over-voltage under condition of high frequency arc extinction theory increases with the increase of arc re-ignition times, which is larger than the historical measured value; in the case of hybrid arc extinction, the more times high frequency arc extinction occurs and occurs continuously, the larger the maximum transient over-voltage is; when arc grounding fault occurs in mine power supply system, power frequency arc extinction and high frequency arc extinction alternately occurs, and probability is very low that high frequency arc extinction continuously occurs more than three times.