The DC short-circuit fault current cannot be blocked by the modular multilevel converter (MMC) with traditional half-bridge sub-module (HBSM), which reduces the reliability of MMC based high voltage direct current (MMC-HVDC) systems. In this paper, based on two HBSM systems, a new bypass sub-module named diode clamp dual-half-bridge sub-module (DCDHBSM) with DC fault current blocking capability is proposed. Compared with other sub-modules possessing DC short-circuit current blocking capability, the proposed DCDHBSM requires fewer power devices and has lower operation loss. Moreover, a DC fault ride-through strategy suitable for DCDHBSM is designed, and sorting algorithm is utilized to balance the post-fault capacitor voltages of the sub?module. The results of simulation based on MATLAB/Simulink and physical experiment show that MMC assembled with the proposed DCDHBSM can quickly block DC fault current and realize fault ride-through.