Abstract: Different inlet/outlet types and header designs were proposed for the conventional rectangular microchannel heat radiator to obtain the optimal geometric parameters and their effects on the flow distribution and heat transfer were numerically studied.Resultsshow that different inlet/outlet types have great impact on the characteristics of flow distribution for the micro heat radiator.Resultshighlight that flow distribution is relatively better for rectangular header and relatively poor flow distribution for the triangular header, and the fluid flow mechanism can be attributed to the interaction of the branching of fluid and the friction offered by the walls of the header. Type I with rectangular header is better than other cases at both fluid flow and heat transfer characteristics. It can improve the heat transfer performance and meet the demand of high heat flux cooling of microelectronic devices.