A determining method for a working voltage of an isolated neutral system, wherein a power system comprises three phase wires and three capacitor banks, one terminal of each capacitor bank is connected to one phase wire, the respective other terminals of the capacitor banks are connected to one another to form a neutral point, and each capacitor bank comprises a plurality of capacitors; and the determining method comprises: periodically sampling a phase voltage of each phase wire, to obtain a plurality of groups of sampling values of real-time phase voltages, wherein each group of sampling values of real-time phase voltages comprises a sampling value of a phase voltage of each phase wire that is obtained by simultaneously measuring each phase wire; determining unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages, wherein the unbalance rate is a ratio between capacitance values of every two phase wires; and determining a working voltage of the isolated neutral system based on the unbalance rates; characterized in that the step of determining unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages comprises: determining unbalance rates K AB and K AC between the capacitor banks based on the following formula: R = X ′ X − 1 X ′ Y wherein X = x 11 x 21 x 12 x 22 x 13 x 23 ⋯ ⋯ x 1 n x 2 n, Y = y 1 y 2 y 3 ⋯ y n, R = K AB K AC, x 1n denotes a value of x 1 obtained in the n th measurement, x 2n denotes a value of x 2 obtained in the n th measurement, y n denotes a value of y obtained in the n th measurement, x 1 = ( V X - V B) x 2 = ( V X - V C), y = V A - V X, V X denotes a sampling value of a zero sequence voltage of the neutral point, V A denotes a sampling value of a phase voltage of a phase-A wire, V B denotes a sampling value of a phase voltage of a phase-B wire, V C denotes a sampling value of a phase voltage of a phase-C wire, K AB = C B C A, K AC = C C C A, C A denotes a capacitance value of the phase-A wire, C B denotes a capacitance value of the phase-B wire, and C C denotes a capacitance value of the phase-C wire. periodically sampling a phase voltage of each phase wire, to obtain a plurality of groups of sampling values of real-time phase voltages, wherein each group of sampling values of real-time phase voltages comprises a sampling value of a phase voltage of each phase wire that is obtained by simultaneously measuring each phase wire; determining unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages, wherein the unbalance rate is a ratio between capacitance values of every two phase wires; and determining a working voltage of the isolated neutral system based on the unbalance rates; characterized in that the step of determining unbalance rates between the capacitor banks based on the plurality of groups of sampling values of real-time phase voltages comprises: determining unbalance rates K AB and K AC between the capacitor banks based on the following formula: R = X ′ X − 1 X ′ Y wherein X = x 11 x 21 x 12 x 22 x 13 x 23 ⋯ ⋯ x 1 n x 2 n, Y = y 1 y 2 y 3 ⋯ y n, R = K AB K AC, x 1n denotes a value of x 1 obtained in the n th measurement, x 2n denotes a value of x 2 obtained in the n th measurement, y n denotes a value of y obtained in the n th measurement, x 1 = ( V X - V B) x 2 = ( V X - V C), y = V A - V X, V X denotes a sampling value of a zero sequence voltage of the neutral point, V A denotes a sampling value of a phase voltage of a phase-A wire, V B denotes a sampling value of a phase voltage of a phase-B wire, V C denotes a sampling value of a phase voltage of a phase-C wire, K AB = C B C A, K AC = C C C A, C A denotes a capacitance value of the phase-A wire, C B denotes a capacitance value of the phase-B wire, and C C denotes a capacitance value of the phase-C wire.