In case of MMC AC-DC voltage withstand test between MMC converter valve ends

the converter is blocked and the capacitor voltage control algorithm is not put into use. Therefore

the voltage equalization characteristics of the VSC sub-module are affected by the system resistance-capacitance（RC）network. According to the recording result of the test

the voltage distribution law of the sub-module between the valve tower layers is high at the top and bottom layers and low at the middle layer

and the sub-module voltage is firstly diverged

and then tends to be balanced. It is found through analysis that the layout of the waterway and the equalizing electrode has large influence on the RC network of the system

and is the main factor causing uneven voltage between the sub-modules in the test. The detailed simulation model of the AC-DC withstand voltage test of the MMC valve tower is set up and the voltage distribution between the sub-modules obtained by simulation is basically consistent with the test

and the maximum voltage unevenness is 3.9% in 10 s test and 8.9% in 3 h test. The research results have provided reliable support for the waterway and equalizing electrode arrangement of the MMC sub-module and has important reference value.