The　geometric　effects　on　the　liquid　flow　are　investigated　in　microchannel　based　on　the　numerical　simulation　method.　Effects　of　geometry　are　shown　obviously　on　the　microflow　by　comparing　the　results　of　different　geometric　characteristics　covered　hydraulic　diameter,　length　and　aspect　ratio.　Thermal　boundary　conditions　are　same　for　different　cases　in　the　numerical　simulation.　The　effects　of　geometric　parameters　on　the　Poiseuille　number　and　the　Nusselt　number　are　investigated.　The　Poiseuille　number　decreases　with　the　increasing　of　the　aspect　ratio　while　the　Reynolds　number　has　no　effect　on　it　for　the　same　aspect　ratio　microchannels.　For　Rehh,　but　Po　does　not　change　when　Dh　is　larger.　The　length　of　the　microchannel　has　no　effect　on　Po　while　Reynolds　number　has　a　little　influence　on　it.　When　Re　is　20-1800,　Nu　is　proportional　to　the　hydraulic　diameter　and　aspect　ratio　of　the　microchannel.　Effects　of　the　length　on　the　Nusselt　number　vary　at　different　Reynolds　number.　The　relation　of　Nu　and　Re　can　be　fitted,　which　is　affected　by　the　geometry　of　microchannels　for　the　same　substrate　and　flow　liquid.　©　2012　Journal　of　Mechanical　Engineering.