Based　on　the　early　experimental　investigation,　further　numerical　analysis　of　fluid　flow　and　heat　transfer　in　micro　pin　fin　heat　sink　are　discussed　in　this　paper　by　utilizing　the　FLUENT,　a　commercial　software.　The　results　indicate　that　the　turbulence　model　of　RNG　k-Ε　is　more　suitable　for　present　experiment　condition　than　other　models.　The　streamline　in　the　micro　pin　fins　is　very　flexuous.　Along　the　streamline,　the　pressure　of　the　fluid　decreases,　while　the　fluid　temperature　increases.　Vortexes　with　different　sizes,　in　which　pressure　keeps　constant　and　temperature　fluctuates　sharply,　are　found　in　the　tail　part　of　the　pin　fins.　The　heat　transfer　coefficient　of　fins　reduces　following　the　direction　of　flow,　however,　the　scope　decreases　gradually　too,　and　reaches　a　minimum　at　some　points.　The　difference　of　heat　transfer　coefficient　between　face　and　back　of　the　fins　reduces　as　the　progress　of　flow.