The peak value of continuous operating voltage（PCOV） of converter valve is an important reference datum for insulation coordination of converter station. Defining the corresponding operating conditions of PCOV is helpful to narrow the calculation range and reduce the calculation time. Consequently

the expression of valve voltage waveform of 6-pulse rectifier is established in different time intervals

and the relationship between valve voltage jump and peak value of valve voltage is analyzed according to the calculation principle of commutation overvoltage. Then the jump time and operation condition for calculating PCOV are demonstrated. The same method is used to analyze the voltage jump of the inverter and it is found that the effect of commutation overshoot on valve peak voltage is much smaller than that of the rectifier. The influence of the adjacent bridge commutation process on the valve voltage waveform of the 12-pulse converter is further deduced. It is clear that the PCOV of the 12-pulse converter valve is not affected by the adjacent bridge commutation process. The side voltage value and jump voltage value of the valve which determine the peak value of valve voltage under a rated working condition and long-term overload working condition are calculated by taking three practical projects with different voltage grades as examples. The conclusion can be drawn that long-term overload mode is recommended as the operation mode of HVDC transmission project and rectification mode as the operation mode of converter when calculating the PCOV of valve.