The　effects　of　fin　width,　cavity　width　and　Reynolds　number　(Re)　on　the　convective　heat　transfer　characteristics　in　the　microchannels　with　cavities　and　fins　were　studied　by　field　synergy　and　entropy　generation　principle.　The　heat　transfer　enhancement　mechanism　of　micro　structures　was　analyzed,　and　the　comprehensive　performance　of　the　microchannel　was　assessed.　The　results　showed　that　the　increase　of　fin　width　and　cavity　width　was　able　to　reduce　the　heat　transfer　synergy　angle,　improve　the　synergy　relationship　between　flow　field　and　temperature　field　obviously　and　enhance　the　convective　heat　transfer.　However,　the　local　vortexes　caused　the　decrease　of　flow　synergy　angle　and　increased　the　pressure　drop　of　the　microchannels;　the　increase　of　fin　width　was　helpful　to　improve　the　energy　utilization　efficiency　and　enhance　heat　transfer　associated　with　the　increase　of　the　entropy　generation　rate　of　fluid　friction;　increasing　the　cavity　width　properly　was　able　to　reduce　the　entropy　generation　rate　of　heat　transfer,　but　the　extremely　large　cavity　width　led　to　the　increase　of　the　heat　transfer　irreversibility　and　flow　friction;　considering　the　pump　power,　relative　fin　width　and　relative　cavity　width,　new　correlation　of　the　thermal　resistance　was　proposed;　the　microchannel　heat　sink　with　relative　fin　width　0.2　and　relative　cavity　width　2　yielded　the　lowest　thermal　resistance　and　the　best　overall　performance.　©　2019,　Editorial　Department　of　Journal　of　Aerospace　Power.　All　right　reserved.