In view of the problems that the modular multilevel converter (MMC) cannot clear the DC side fault, many of the new sub-module topologies are amended on the basis of the traditional half bridge sub-module (HBSM), which uses their own topology characteristics to clear the fault current fast by making the capacitors of sub-modules charged via the fault current when short-circuit fault occurs on DC side. After researching large numbers of new sub-module topologies, this paper designs a new sub-module which ability of current blocking is relatively prominent. And considering the loss characteristics, a hybrid topology combined HBSM with new sub-module is adopted, which are analyzed from the aspects of modulation strategy, harmonic characteristic and properties of fault blocking. The expression of each harmonic voltage amplitude is deduced and the practicability is verified by simulation analysis. This work is supported by State Grid Science and Technology Program in 2014 "Key Techniques Research and Demonstration Application of Flexible Loop Network Controller" (No. 2014GW-05).