Coupled heat and mass transfer processes between moist air and water/aqueous solution commonly occur in absorption/desorption systems for air conditioning, thermal storage and energy conservation, which are always optimized from such two aspects as layout synthesis and parameter matching. This contribution introduces six sub-zones in the integrated property diagram of moist air and aqueous solution according to the differences of temperatures, absolute humidities and relative humidities between moist air and water/aqueous solution, and describes different heat and mass transfer characteristics between them in each sub-zone, which favor the construction of different optimal layouts and their corresponding systems to make full use of heat and mass transfer potentials. Based on the optimal layouts, a quantitative method for the system parameter matching is further proposed based on the conditional extremum method in mathematics. The optimized results of a typical liquid regeneration system show that utilization of the proposed optimization method gives the optimal allocation of mass flow rates of all working fluids to minimize the total mass flow rate with a constant required mass transfer quantity and increasing the inlet temperatures of moist air, liquid desiccant and regeneration medium reduce the total mass flow rate of all working fluids. (C) 2015 Elsevier Ltd. All rights reserved.