Abstract: Numerical simulations and analysises were presented on heat transfer characteristic for combined micro pin fins heat sink which consisted of circular pin fins with isosceles right-angled triangle pin fins on both end sides.The numerical results were analyzed according to different attack angle arrangements of right-angled triangle pin fins.Comparing with micro circular pin fin heat sink,the heat transfer for combined micro pin fin heat sinks is improved greatly.In addition,the computational evaluations indicate that the heat transfer enhancement effect of combined micro pin fin heat sink with the attack angle 30° is the most significant.However,the heat transfer enhancement effect is decreased as Re increased.