Abstract: To deal with short-circuit faults on the DC side of modular multilevel converter (MMC), a topology of freewheeling path blocking sub-module (FPBSM) for MMC with fault current transfer function is studied. Based on the summary and classification of MMC sub-modules with the capability of clearing fault current, the topology of FPBSM is deduced. The freewheeling path is eliminated based on the unidirectional conduction characteristic of diodes, and the fault current can be eliminated by cooperating with the thyristor at the port and the control strategy. FPBSM can improve the ability of fault current clearing and ensure that the capacitor voltage is balanced on the premise of economy. Based on MATLAB/Simulink simulation model and hardware experiment system, the fault current clearing capability of FPBSM-MMC is verified.