A new method is proposed to measure the capacitive and impedance current of resonance grounding power networks based on phase modulation of zero-sequence voltage. For the arc suppression coil and damping resistance in parallel grounded power networks, the grid-to-earth capacitance and resistance can be calculated accurately through switching the parallel damping resistor to increase the damping rate, while adjusting the inductance of arc suppression coil to guarantee phase difference of zero sequence voltage be 90 degrees before and after the adjustment. The simulation model is established and experiments are carried out in MATLAB to verify the correctness of this tuning method. The tuning method is simple, implemented easily, and can be used in not only the follow-resonant arc-suppression but also the pre-resonant one.