Abstract: Aiming at the problem of personal electric shock current exceeding the standard of frequency converter power supply system in coal mine, based on the safety threshold of 30 mA · s, the simulation model of low voltage power supply network with frequency converter is constructed by MATLAB / Simulink, and the mechanism of electric shock current surge caused by the coupling of high frequency harmonics and distributed capacitance caused by SPWM modulation of frequency converter is revealed. The theoretical derivation shows that the effective value of the electric shock current is 802.7 mA by establishing the breaking linear model. It is verified that cutting off the power supply within 37 ms can control the electric shock energy within the safe range and meet the three-level electrical safety standard. The research results provide a theoretical basis for the optimization of leakage protection setting value of frequency conversion power supply system in coal mine, and have engineering guiding significance for ensuring the safety of underground operation.