The wavy surface of a falling film has a significant effect on the heat/mass transfer of liquid desiccant dehumidification systems. This paper developed and analytically solved a 2D theoretical model for predicting the time-series surface waves of falling film desiccant dehumidification process. The influences of operating conditions, physical properties of desiccant and air, vapor pressure and thermocapillary forces due to interfacial mass transfer, and the interaction between the desiccant and working plates were considered. The model was validated by experiments with an acceptable error of 10.9% for the frequency, 6.59% for the amplitude and 14% for the contact area changing rate. The actual changing rate of liquid/air contact area with time could be predicted with this model, which was 20-90% higher than the flat film assumptions at a solution mass flow rate from 0.0126 to 0.043 kg/s. Then, parameter analyses of fluctuating desiccant film were numerically performed. Although increasing the temperature or decreasing the concentration of a liquid desiccant increased the wave intensity, the mass transfer driving force was also reduced, which is not suitable for practical systems. However, if the surface tension dropped to the original 10-50% by surface modification or surfactant addition, then the contact area could increase by approximately 10-40% due to the surface wave enhancement. In addition, this method is cost efficient and has little impact on the system structure. Therefore, with this model, it is theoretically possible to evaluate the time-series characteristics of a wave-wise liquid/air interface with heat and mass transfer, which could improve the evaluation accuracy of falling film liquid desiccant dehumidification systems. Thus, this study effectively helps the prediction and optimization of practical dehumidification systems, and other applications related to gas/liquid flow. (C) 2018 Elsevier Ltd. All rights reserved.