The dew point Indirect Evaporative Cooling (IEC) achieved through Maisotsenko cycle (M-Cycle) is a complicated thermodynamic process. For further understanding of the heat and mass transfer occurred in a dew point indirect evaporative air cooler with M-Cycle counter-flow configuration, the paper presents a novel mathematical model that combined the law of energy conservation and the principle of the irreversible thermodynamic theory. The model, comprising of numerous mass, energy and entropy equations, was used to carry out the parametric study of the dew point air cooler under various operational and structural conditions. The entropy production number is found to be a promising indicator for optimized design. Through the combined analysis of energy efficiency and thermodynamic irreversibility of the target IEC system, the recommended average air velocity in dry channels should be less than 1.0 m/s, the channel length should be in the range of 1-1.75 m and the channel gap should be controlled to 3-5 mm, while the working to intake air ratio should be around 0.3-0.4. The modeling analysis has provided a theoretical perspective of irreversible degree of energy utilization for thermal analysis of dew point IEC, and thus laid the theoretical foundation for the optimization design of this kind of cooler. (C) 2019 Elsevier Ltd. All rights reserved.