The laminar flow and heat transfer of water in periodic fully-developed divergent-convergent channels has been investigated numerically.The SIMPLE algorithm and body-fitted coordinates (BFC) are used.The periodic boundary condition is treated using the method proposed by Amano.It is found that under the range of Re=100~1 000,the friction factor is about 10%~200% more than that of parallel plate channel,while the average Nusselt number is about 40%~320% more than that of parallel plate channel.