Abstract: In order to identify the AC bus with the largest voltage drop under the same power transfer and the DC system with the greatest impact on the voltage of the same AC bus,and identify the AC disconnection fault with the largest steady-state voltage rise,the influence of external transmission system fault on AC voltage in UHV AC/DC hybrid power grid was theoretically deduced and simulated.The mathematical model of AC/DC hybrid transmission system was established,the influence of AC channel and DC channel faults on AC voltage was analyzed,and theoretical calculation was carried out.The simulation model of UHV AC/DC hybrid power grid in Ximeng area was built based on PSASP,and the accuracy and effectiveness of the theoretical calculation results were verified by simulation.The simulation results show that the greater the equivalent resistance from converter bus to AC bus,the greater the voltage drop of AC bus caused by DC blocking,the greater the ratio of transmission reactive power to head end voltage,and the greater the voltage rise at the head end of the line in case of AC single circuit disconnection fault.This study provides theoretical guidance for the control of steady-state operation voltage of the system,and is of great significance for the safe and stable operation of AC/DC hybrid system.