Abstract In general, constant flow rates are assumed for thermal design of heat exchangers. However, the constant flow rates are not available in the heat exchangers used for fan-supplied systems. In this paper, a coupling e-NTU method is presented to calculate the cooling efficiency of a fan-supplied cabinet cooling system, in which the pressure-flow rate characteristics of the fans and heat exchanger are considered simultaneously. The effects of heat exchanger parameters on the cooling efficiency of the cabinet cooling system are studied. It is found that the cooling efficiency of the system obtained by the coupling e-NTU method is significantly different from that obtained by the traditional e-NTU method. Therefore, it is necessary to using the coupling e-NTU method for the heat exchanger thermal design in the cabinet cooling system.