The converter valves play crucial roles in high voltage direct current transmission (HVDC). However, converter valves contain fully-controllable power semiconductor devices, e.g., the gate bipolar transistors (IGBT), and the power diodes, which usually operate under high-frequency state. The resultant dramatic changes of voltages and currents cause severe radiated electromagnetic interference (EMI), which is one of the major concerns of HVDC. In this paper, the radiated EMI of an experimental converter valve is numerically investigated via FEM simulation, and measured by a proposed antenna-based testing system. The simulated and measured EMI results exhibit good agreement. In addition, the results indicate that though the electric field intensity at the surface of submodules can be intense, the radiated EMI decay rapidly in the air, and the maximum value of the radiated Ez is roughly 120 V/m at an observation point 75 cm away from the tested valve section.