In this paper, the influence of four different entrances and exits to flow maldistribution in air-cooled heat exchangers is presented. The flow and heat transfer are computed by the numerical solution of the governing partial differential equations including the conservation equations of mass, momentum and energy. The flow maldistribution of each heat transfer tubes of four different cases are analyzed, so as the heat transfer rate. The heat transfer rate average deviation is much smaller than flow average deviation. Slight differences of total heat transfer rate are found for different cases. The reason of this phenomenon is related to the relationship between flow and heat transfer rate and the heat resistance distribution. The flow pattern in different tubes and the resistance performance of different cases are compared.