Aiming　at　the　problems　of　high　peak　value　of　fault　current，fast　rising　speed　and　unable　to　ensure　the　reliability　of　power　supply　in　non-fault　area　in　multi-terminal　DC　system，a　fault　isolation　strategy　based　on　the　cooperation　of　a　cascaded　novel　flexible　current　limiter　and　a　mechanical　DC　circuit　breaker　is　proposed，which　is　suitable　for　the　medium　and　high　voltage　distribution　network.　Firstly，the　flexible　current　limiter　is　triggered　by　differential　undervoltage　protection　to　achieve　the　effect　of　inter-pole　voltage　clamping，suppress　the　fault　current　and　improve　the　dynamic　recovery　characteristics　of　DC　system　after　fault　isolation.　Secondly，according　to　the　breaking　speed　of　DC　circuit　breaker，the　action　time　of　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　area　until　the　circuit　breaker　acts　to　isolate　the　fault.　This　strategy　can　also　avoid　the　blocking　of　converter　station，reduce　the　requirements　of　breaking　speed　and　breaking　capacity　of　circuit　breaker，prolong　the　service　life　of　circuit　breaker　and　improve　the　reliability　of　system　power　supply.　Finally，a　four-terminal　medium　voltage　distribution　network　model　is　built　in　MATLAB／Simulink，and　the　effect　of　current　limiter　and　the　feasibility　of　the　proposed　strategy　are　verified　by　simulation.　©　2023　Electric　Power　Automation　Equipment　Press.　All　rights　reserved.