This　paper　develops　a　dynamic　electromechanical　coupling　model　to　investigate　the　energy　harvesting　(EH)　performance　of　the　vibro-impact　(VI)　energy　harvester　comprising　a　cylindrical　capsule,　an　internal　free　moving　ball,　and　two　dielectric　elastomer　(DE)　membranes　at　both　ends　of　the　capsule.　The　developed　model　can　describe　the　electromechanical　properties　of　the　collision　between　the　ball　and　the　membrane,　which　is　verified　by　the　existing　experimental　data.　On　this　basis,　the　effect　of　system　parameters,　such　as　the　mass　and　the　radium　of　the　ball,　the　internal　radium　and　the　length　of　the　capsule,　and　the　pre-stretch　ratio　of　DEs,　on　the　average　power　density　of　the　energy　harvester　is　also　studied　under　diverse　external　stimuli　including　the　inclined　angle　and　the　excitation　frequency.　The　results　show　that　at　the　small　excitation　frequency,　the　EH　performance　of　the　energy　harvester　can　be　improved　by　increasing　the　pre-stretch　ratio　of　membranes　and　the　mass　of　the　ball　and　decreasing　the　radium　of　the　ball　and　the　internal　radium　of　the　capsule.　The　conclusions　can　help　provide　a　guide　for　the　optimal　design　of　the　energy　harvester　in　the　practical　application　so　as　to　improve　the　EH　performance.