By using the CFD software and combining with experimental studies we conduct the three-dimension numerical investigation on the characteristics of flow and heat transfer in microchannel heat sink with circular,triangle and square cross-section pin-fin arrays.The flow field and temperature field of the three types pin-fin arrays are obtained for different Reynolds number(Re). Besides,the friction coefficient(f)and Nusselt number(Nu) have been calculated as the criterion of the flow and heat transfer properties of micro pin-fin. The results show that the friction coefficient decreases with the increase of Re,that the frictional resistance coefficient of triangle pin-fin is the smallest with low Re. And that the Nu grows with the increase of Re,and the Nu of circular pin-fin is larger than that of triangle or square,which appears a better heat transfer performance. The assesses of the comprehensive flow and heat transfer performance indicate that the circular pin-fin has better performance than the others. Furthermore,compared with experimental outcome,the numerical results still have some deviation owing to microscale effect while the trend is consistent with experimental results.