Coupling capacitors are important equipment in electric power system which are used for high-frequency protection, voltage measuring and over voltage suppression for grid. Because of its structure, coupling capacitor always exists residual inductance, which affects the coupling capacitor’s high frequency performance. In this paper, the formation mechanism of residual inductance is studied, and measured by IM 3570 impedance analyzer, the test results indicate that the residual inductance of coupling capacitor is comprised of two parts, one part is the inductance of flange and aluminum foil electrode, the other part is the inductance of lead wire. On this basis, three sets of coupling capacitors with different size of lead wire are developed, and the residual inductance measuring results indicate that the residual inductance of coupling capacitor is related to the size of lead wire, more wide the lead wire is, more smaller the residual inductance is. The study result has practical significance for improving the high frequency performance of coupling capacitor.