Abstract: In order to solve the calibration problem of the 500 kV voltage transformer test platform with resonant reactor that can not be disassembled,a series resonant circuit was proposed to boost the voltage by matching the resonant reactor with the high voltage capacitor.The principle of series resonant boost was introduced,and the configuration of resonant capacitor,current monitoring of primary circuit and calibration circuit of test platform were analyzed.The application test of the test platform was carried out and 10 independent repeatability measurements were made under the condition of repeatability. The uncertainty evaluation was carried out from three aspects:measurement repeatability,main standard and measurement data modification of the test platform.The combined standard uncertainty and expanded uncertainty were calculated and verified by transfer comparison method,and the error distribution interval was determined.This study provides a reference for the calibration method of voltage transformer with resonant reactor which can not be disassembled.