First of all, this article expounds the capacitive current to the harm of coal mine power grid and introduces the commonly used method of capacitance current measurement. The signal injection method in the calculation of the capacitance current, often ignore the existence of unbalanced voltage. Based on the signal injecting method，the capacitive current measurement results will produce large errors due to the presence of unbalanced voltage, In order to improve the measurement precision and eliminate the influence of the unbalance voltage, a no phase locked loop filter method is used. Using the standard sine, cosine signal instead of the phase-locked loop filter method. The method can accurately filters out the imbalance voltage signal and improves the capacitance current measurement precision. When the unbalanced voltage is eliminated, the capacitance measurement accuracy has been improved in MATLAB simulation.