The performance of air dehumidifiers using LiCl solution as the liquid desiccant was studied. A mathematical model describing heat and mass transfer performance of cross and counter flow dehumidifiers was set up and the analytical solution of differential equations was derived. The parameter distributions of air and desiccant were stated. The results showed that the mathematical model can be of great value in the design and improvement of cross and counter flow dehumidifiers. The analytical solutions can be utilised in the optimisation of the cross and counter flow dehumidifiers.