The　performance　of　a　new　type　of　latent　heat　thermal　energy　storage　(LHTS)　device　based　on　flat　micro-heat　pipe　arrays　(FMHPAs)　with　longitudinal　rectangular　fins　is　numerically　studied　by　enthalpy-porosity　technique　based　on　finite　volume　method　(FVM)　in　this　research.　The　numerical　model　is　verified　correct.　The　temperature　distribution　and　phase　transition　process　in　different　directions　of　the　interior　of　a　thermal　storage　tank　and　the　effects　of　fin　height,　spacing,　and　thickness　on　charging　power　and　thermal　storage　capacity　are　also　analyzed　numerically.　Results　show　that　phase　interface　is　presented　in　U　type　in　the　horizontal　direction.　In　the　vertical　direction,　the　phase　change　material　(PCM)　among　fins　melts　from　up　to　down　when　the　fin　spacing　is　larger　than　6　mm,　and　the　opposite　occurs　when　the　fin　spacing　is　less　than　6　mm.　The　thermal　storage　capacity　of　the　LHTS　device　is　reduced　drastically　when　the　fin　spacing　is　less　than　4.14　mm.　For　fin　height,　the　structure　of　multiple　rows　of　FMHPAs　with　dwarf　fins　is　recommended　because　it　exhibits　large　power　and　exerts　a　small　negative　effect　on　thermal　storage　capacity.　Fin　thickness　has　a　minimal　effect　on　charging　power　and　thermal　storage　capacity.　The　study　results　provide　optimization　design　guidance　for　LHTS　devices　based　on　FMHPAs　under　various　application　backgrounds,　such　as　solving　the　contradiction　between　energy　supply　and　demand　in　solar　thermal　systems　and　the　peak　load　shifting　of　electricity　in　heat　pump　systems.