DC-side　faults　are　the　key　issue　of　HVDC　transmission　based　on　modular　multilevel　converters(MMC),　and　in　particular　HVDC　transmission　is　popularized　for　overhead　line　applications.　In　this　paper,　the　characteristics　of　DC　short-circuit　faults　are　studied　for　a　flexible　DC　power　system.　The　half-bridge　MMC　fault　equivalent　circuit　is　established　and　the　corresponding　over-current　analytical　equation　is　deduced.　The　working　mode　of　the　hybrid　DC　circuit　breaker　breaking　fault　current　is　studied.　A　hybrid　DC　circuit　breaker　is　used　to　propose　a　line　reclosing　strategy.　On　the　PSCAD/EMTDC　platform,　a　DC　grid　system　simulation　model　was　built　to　verify　the　effectiveness　and　feasibility　of　the　proposed　scheme.　The　results　show　that　after　the　hybrid　circuit　breaker　recloses,　within　0.1s,　the　power　of　each　converter　station　recovers　and　maintains　stable　operation.　The　DC　grid　can　cross　the　short-circuit　fault　quickly　and　steadily.　©　2019,　Electrical　Technology　Press　Co.　Ltd.　All　right　reserved.