The performance of air dehumidifier using LiCl solution as the Liquid desiccant was studied with numerical methods. A mathematical model describing heat and mass transfer performance of air dehumidifierwas set up. The numerical solution of differential equations were derived. Taking the heat and mass transfer coefficients obtained by experiments as the input parameters of the model，the parameter distribution of air and solution was described. The simulation results corresponds very well to experimental data. Simulation results indicated that the mathematical model could be used to predict the performance of air dehumidifier. The results showed that the mathematical model can be of great value in the design and improvement of air dehumidifier.