Proton exchange membrane fuel cells requires humidification the reactive gases before entering the fuel cell for good performance. Using a planar membrane humidifier with important advantages such as simple building and no moving parts, is one of the best methods to humidification the reactive gases discussed in this paper. In this study, it is proposed to insert porous layers (gas diffusion layers) on both sides of the membrane, to increase the residence time gases. Therefore, by using three-dimensional and numerical modeling of the humidifier, the effect of porous layers and the effect of their properties on the humidifier performance are investigated. For this purpose, a non-porous humidifier is first modeled, and then the porous layer is inserting on the wet side, on the dry channel side, and on two sides of the membrane, and the performance of these models is compared. The results show that the highest dew point temperature of dry side outlet is related to the use of gas diffusion layers on both sides, on the dry side, on the wet side and humidifier without gas diffusion layers respectively. In all cases of laying gas, with increasing porosity coefficient and permeability, dew point increase and improve humidifier performance.