Accurate and effective measurement of harmonic voltage is an important prerequisite and basis for mastering the harmonic status of a power grid, carrying out harmonic control and improving the level of power quality. In order to solve the problem that a large number of currently running CVT cannot accurately measure harmonics, a harmonic voltage measurement method based on CVT capacitor current is proposed. This method measures the current flowing through the high voltage capacitor and the middle voltage capacitor branch and carries out harmonic analysis. Given the capacitance parameters, the high voltage side harmonic voltage can be calculated conveniently and accurately. This method only needs simple modification of the CVT secondary circuit to realize harmonic voltage measurement without affecting the safety of the equipment. First, the basic principle of this method is given, and then the influence of current measurement accuracy and capacitance variation on harmonic measurement error is analyzed by simulation. The physical test verification of actual CVT is completed. Test result shows that the measurement errors of 2-50 harmonic voltages are less than 2%, which meets the relevant requirements of harmonic national standards. This work is supported by Science and Technology Project of State Grid Corporation of China (No. 5200-201924064A).