In this paper, the effect of the wall roughness on the water behavior related to the PEMFCs gas channel is investigated by the two-phase flow simulation. And. the different wetting conditions of the wall surface are considered. i e hydrophilic surface and hydrophobic surface. The relative roughness height and the roughness element density as well as the roughness element type are also considered in the Study And the results show (1) for hydrophilic Surface, water behavior for smooth case is different from the roughness cases, due to the effect of roughness oil the water slug morphology even for r/H = 0.2% toughness (2) r/H = 0.2% is positive for water removal and will not lead to the high pressure drop for hydrophilic surface, (3) r/H = 5% is advantageous for water removal for hydrophilic Surface but disadvantageous for hydrophobic case. and the pressure drop greatly increases for both cases. (4) for hydrophobic surface, roughness of r/H = 1% and r/H = 2% slow down the water removal speed. but will not affect the amount of the removable water, (5) there is nearly no effect for r/H = 0.2% for hydrophobic case, (6) for both conditions. the average pressure drop obviously increases when r/H >= 2%. (7) Increase of the roughness element can help water removal for hydrophilic case but no Obvious function for hydrophobic SUI face (8) The triangle roughness element is better than rectangle element with the same height (C) 2009 Elsevier B V All rights reserved