Abstract: In view of the inability of the modular multilevel converter（MMC）in the high voltage direct current（HVDC） transmission projects in current operation to lock fault current on the DC side,an MMC topology based on clamp double sub- module（CDSM）capable of automatically eliminating and restarting the fault current on the DC side is analyzed.Because of the reverse blocking of diodes,blocking during a DC fault is achieved by blocking all the impulses of IGBTs,then the DC fault is eliminated without the action of AC breakers.Simple in structure and economical,this topology combines the modulation and the control strategy of MMC based on half bridge sub-module（HBSM-MMC）with the ability of recovering from a DC fault.A comparison with the HBSM-MMC in the case of a DC pole-to-pole fault by simulation and analysis has proved the performance of MMC based on CDSM in the control of DC fault current.