In order to accurately predict the radiated electromagnetic disturbance generated during the normal operation of an extra-high voltage (EHV) large-capacity VSC-HVDC transmission system, this article studies the electromagnetic radiation problem based on a certain ±800 kV modular multilevel converter (MMC) valve in China. First, the disturbance source of the VSC-HVDC converter valve is analyzed. A new calculation method based on the complex geometric structure of the converter is proposed that uses DC bus current as the disturbance source. Then the antenna model with reference to the actual structure of the converter valve is built in FEKO. The radiated electric field and magnetic field strength generated in a valve hall of the converter are calculated, and the variation of electromagnetic disturbance with distance at different frequencies is analyzed. The calculation method and results can be used to guide electromagnetic disturbance research of UHV large-capacity VSC-HVDC transmission systems.