Abstract: Under the influence of the phase-controlled characteristic of the fault current of the flexible DC converter, the traditional distance protection is prone to incorrect operation behavior after a single-phase grounding fault through a transition resistance occurs in the AC transmission line of flexible DC. This paper analyzes the distribution law of electrical quantities when a single-phase grounding fault occurs in the AC transmission line of flexible DC. Using the characteristic that the negative-sequence current on the converter station side is suppressed during the single-phase grounding fault of the AC transmission line of flexible DC, a new type of single-phase grounding distance protection based on comprehensive sequence components is proposed. The proposed protection scheme eliminates the influence of transition resistance theoretically and can accurately calculate the fault location based on singleend quantities. Moreover, this protection is also suitable for the scenario that flexible DC is integrated into a weak system. Finally,the effectiveness of the proposed protection scheme is verified through simulation.