Abstract: For problem that resonance point is difficult to determined which lead to measuring error of capacitive current when arc suppression coil with three phases and five columns in coal mine power grid is tuned by use of resonance method, an improved tuning method was proposed. Admittance triangle composed by fixed side of edge-to-ground conductance and variable sides of edge-to-ground susceptance and admittance according to characteristics of damping ratio unchanged and out-of-resonance degree changed in tuning process. Capacitance current is calculated according to change of admittance angle. The simulation and experimental results show that the improved tuning method has higher measuring accuracy than the resonance method, and measuring error decreases with increase of damping ratio.