A　passive　micromixer　with　gaps　and　baffles　was　proposed　based　on　the　principle　of　chaotic　mixing　and　the　fluid　flow　and　mixing　characteristics　in　the　micromixer　were　studied　by　three-dimensional　numerical　simulation　and　visualization　experiment.　Expanded　vortices　and　separated　vortices　were　generated　in　the　horizontal　plane　and　counter-rotating　vortices　formed　in　the　cross-sectional　plane　perpendicular　to　the　flow　direction　by　the　combination　of　gaps　and　baffles.　The　mixing　efficiency　was　significantly　improved　by　the　multidirectional　vortices.　The　geometrical　parameters　of　gaps　and　baffles　had　great　effect　on　the　fluid　flow　and　mixing.　Based　on　the　consideration　of　mixing　efficiency　and　pressure　drop,　the　effect　of　gap　width,　gap　length　and　baffle　height　on　the　comprehensive　performance　of　the　micromixer　was　investigated　by　the　field　synergy　principle.　The　optimal　structural　parameters　were　presented　with　varying　Reynolds　number.　©　All　right　reserved.