To　investigate　inflow　fields　in　Micro-channel　at　Reynolds　number　lower　than　1,　such　as　inflow　in　vascular　plant,　with　micro-fluidic　particle　image　velocimetry　(Micro-PIV)　technique　and　numerical　simulation　that　simulating　wall　roughness　elements　by　setting　up　porous　medium　thickness　and　momentum　source　of　porous　medium　model　in　software　Fluent,　inflow　fields　in　straight　micro-channels　with　cross　section　of　400　μm×400　μm　under　the　conditions　of　the　Reynolds　number　of　0.15,　0.25　and　0.35　were　obtained　respectively.　The　velocity　distributions　were　compared　with　analytical　solution　adopted　by　solving　governing　equations　directly.　The　result　shows　that　effect　from　wall　roughness　on　the　velocity　distributions　is　small　but　not　ignorable　in　micro-channel,　so　the　analytical　solution　cannot　meet　the　experimental　results.　The　profile　has　the　same　tendency,　but　the　value　is　lower　in　the　mean　flow　area,　which　is　distant　from　horizontal　axis　less　than　0.04　mm,　and　higher　in　other　region　near　the　wall.　Velocity　distributions　derived　by　the　numerical　simulation　meet　the　experimental　results　well,　so　this　numerical　simulation　can　be　successfully　used　in　handling　inflow　problems　at　low　Reynolds　number　in　square　section　straight　micro-channel.