The　geometries　of　wicking　structure　of　flat-plate　micro　heat　pipes　(FPMHPs)　determine　the　capillary　force　and　quantity　of　working　fluid,　which　remarkably　affect　thermal　performance.　In　this　study,　flat-plate　micro　heat　pipes　(FPMHPs)　with　different　geometries　were　designed　and　fabricated,　and　their　heat　transfer　characteristics　were　compared.　Results　showed　that　the　thermal　performance　of　the　FPMHPs　was　relatively　weak　M　alpha　=　0　degrees　because　the　condensate　backflow　can　only　be　driven　by　capillary　force.　At　alpha　=　90　degrees,　the　A-4-type　FPMHP　presented　the　best　performance　under　the　common　joint　effect　of　capillary　force,　gravitational　force,　and　the　quantity　of　working　fluid.　The　minimum　thermal　resistance　and　the　maximum　thermal　conductivity　of　this　FPMHP　were　0.89　K/W　and　1739.98　W/(m.K),　respectively.　A　visualization　study　was　also　conducted　to　validate　and　investigate　the　heat　transfer　process　of　the　vapor-liquid　phase-change　and　the　heat　transfer　limit　in　the　FPMHP.　We　found　that　a　slug-train　unit　formed　when　the　heating　power　was　sufficiently　large,　causing　a　local　dryout　phenomenon.　The　evaporation　section　presented　a　complete　dryout　with　the　further　increase　in　heating　power.　Therefore,　the　heat　transfer　limit　in　the　mini/micro　FPMHP　was　dependent　on　the　dryout　limit.