Provided in the invention is an MMC sub module with the direct-current fault blocking capability. The MMC sub module comprises a power electronic device and a capacitor. A hybrid bridge arm formed bya plurality of MMC sub modules form a flexible direct-current power transmission converter; and a rectification or inversion function can be realized in normal operation. When a direct-current bus short-circuit fault occurs at a direct-current side of the converter, a power electronic switch is turned off and the capacitor is connected in series to a clamping diode in a reverse direction to realize direct-current bus fault isolation. Therefore, the short-circuit reverse current fault isolation capability of the flexible direct-current power transmission direct-current side based on a damping dual-sub-unit module is improved.