Recently,　the　stability　of　DC　microgrids　has　attracted　increasing　attention.　The　traditional　stability　analysis　method　cannot　not　meet　the　requirements　for　the　complexity　and　bidirectional　energy　flow　of　the　system.　In　this　paper,　a　passivity-based　stability　criterion　(PBSC)　is　proposed　to　analyze　the　stability　of　the　cascade　system.　In　order　to　realize　the　passivity　of　the　system,　an　improved　feedback　control　method　based　on　the　traditional　double-loop　control　strategy　is　proposed,　which　will　improve　the　stability　region　and　guarantee　the　passivity　of　the　system.　Moreover,　a　Buck-CPL　simulation　model　is　established　based　on　MATLAB/Simulink　R2008,　and　the　correctness　of　the　theoretical　analysis　is　verified　by　experiments.