In order to solve the problems that the scope of the measurement range of capacitance is limited and to select the proper frequency is difficult, based on the phasor method, a novel method is proposed and the frequency selection and error analyses are given as well. In the improved method, a high and a low frequency amplitude constant voltage signals are injected into PT open delta side, and the zero sequence current of the open the triangle side is measured. According to the equivalent circuit of the distribution network, the capacitance is calculated. Through theoretical analysis and simulation verification, the improved method has the advantages of simple operation and high measuring precision, and is suitable for the capacitance measurement of larger systems.