Electromagnetic radiation is a serious threat to electronics components in high-power systems. Measurement of the magnetic field in the real high-power facility is needed. In this paper, the magnetic field in a high-power MMC mutual driving system has been measured from 1 Hz to 30 MHz with two near-field probes with different frequency ranges. By analyzing and comparing the magnetic fields at different positions near the submodule inside the MMC valve tower under different operating conditions, the characteristics of magnetic field interference inside the valve tower are analyzed, and the main interference source components in different frequency ranges and the variation of magnetic field intensity with operating conditions are confirmed.