This paper proposed a two-dimensional numerical model for the heat and mass transfer process in dew-point evaporative cooler with porous layer covering the wet surface. Water flows down along the wet surface covered by a fibrous layer which can intensify the water wettability and increase the wetting area, and transfers the heat and water vapour with secondary air in wet channel and heat with primary air in dry channel. The water downward flow in porous layer is governed by Darcy-Brinkman Equation and the heat and mass transfer in gas-liquid interface is derived from the molecular dynamics equation. The coupled momentum and heat and mass transfer equations for primary air, water and secondary air are solved by COMSOL. The distribution of temperature and heat distribution and the influence of porosity of the porous fibrous layer, inlet air velocity, working-to-primary air ratio and water inlet velocity and temperature on heat and mass transfer between the water and air are numerically studied and analysed. The numerical results showed that the influence of porosity of the porous layer is not significant, but the inlet air velocity and working-to-primary air ratio and water inlet velocity and temperature influence the cooling performance of dew-point evaporative cooler a lot.