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 m·s-1，the optimized structural parameters were 0.15<L1/L2<2 and 1.4<W2/W1<2.1.