Due　to　the　design　of　fan-shaped　reentrant　cavities,　the　microchannel　with　periodically　changeable　cross-sections　is　divided　into　constant　diameter　region　and　arcuate　region.　The　structural　parameters,　including　the　lengths　and　widths　of　the　constant　diameter　region　and　the　arcuate　region　have　an　important　influence　on　the　behavior　of　fluid　flow　and　heat　transfer　in　the　microchannel　with　periodically　changeable　cross-sections.　The　influence　of　structural　parameters　with　three-dimensional　numerical　analysis　was　investigated　in　this　paper.　The　steady,　laminar　flow　and　heat　transfer　equations　were　solved　by　using　a　finite-volume　method.　The　analysis　showed　that　the　influence　of　different　structural　parameters　on　fluid　flow　and　heat　transfer　was　very　significant.　When　u=4　ms-1,　the　optimized　structural　parameters　were　0.151/L22/W1