In　this　paper,　by　utilizing　CFD,　numerical　simulations　and　analyses　were　used　to　research　the　flow　and　heat　transfer　characteristic　in　different　porosity　staggered　circular　shaped　micro　pin-fin　heat　sinks　whose　hydraulic　diameter　is　200　μm.　The　results　indicate　that,　with　the　increase　of　Reynolds　number,　vortexes　with　different　structures　are　found　in　the　pin　fins　wake　zone.　Under　different　porosity,　the　size　and　shape　of　vortexes　are　different　due　to　the　influence　of　pin-fins　at　downstream.　The　influence　on　Nusselt　number　of　the　heat　sinks　caused　by　the　change　of　heat　flux　is　different　under　different　porosity.　There　is　barely　influence　on　Nusselt　number　under　smaller　porosity　when　heat　flux　changes,　while　under　larger　porosity,　the　Nusselt　number　increases　with　the　increase　of　heat　flux.　©　2017,　Science　Press.　All　right　reserved.