Aiming　at　the　problems　of　high　peak　value　fault　current,　fast　rising　speed,　and　being　unable　to　ensure　the　reliability　of　the　power　supply　in　the　non-fault　zone　in　a　multi-terminal　DC　system,　a　new　cascade　flexible　current　limiter　and　mechanical　DC　circuit　breaker　for　medium-　and　high-voltage　distribution　networks　are　proposed.　Firstly,　the　flexible　current　limiter　is　triggered　by　differential　under-voltage　protection　to　achieve　the　effect　of　interpole　voltage　clamping,　suppressing　the　fault　current　and　improving　the　dynamic　recovery　characteristics　of　the　DC　system　after　fault　clearing.　Secondly,　according　to　the　breaking　speed　of　the　DC　circuit　breaker,　the　action　time　of　the　current　limiter　can　be　set　flexibly.　The　directional　pilot　protection　signal　of　the　circuit　breaker　is　used　to　ensure　the　continuous　action　of　the　current　limiter　at　the　converter　station　side　in　the　fault　zone,　until　the　circuit　breaker　acts　to　isolate　the　fault.　The　protection　strategy　can　also　avoid　the　blocking　of　the　converter　station　and　reduce　the　requirements　for　the　breaking　speed　and　breaking　capacity　of　the　circuit　breaker.　Finally,　a　four-terminal　medium　voltage　distribution　network　model　is　built　in　MATLAB/SIMULINK,　and　the　effect　of　the　current　limiter　and　the　feasibility　of　the　proposed　protection　strategy　are　verified　by　simulation.