In the present study, water is considered to be in vapor state when intruding the gas diffusion layers (GDL) of proton exchange membrane fuel cell (PEMFC). A phase change solver was developed in OpenFOAM platform and validated to model the vapor condensation processes in reconstructed GDL. The stochastic method was adopted to reconstruct the 3D GDL while the vapor/condensate water two-phase flow problem was solved by employing the volume of fluids (VOF) method. Vapor condensation processes in GDL with/without rib were compared under different current densities and ambient temperatures. The temporal varying condensate droplets' distributions were displayed and the droplets evolution processes were summarized. Vapor condensation processes can be divided into several stages, including small water-droplets generation, droplets growth, coalescence, accumulation, and condensate water removal. It was found that the condensate water distribution under the rib was entirely different from that under the channel. Water saturation in GDL without rib was lower at the same current density and same ambient temperature. In addition, the vapor condensation was highly sensitive to the local temperature. Growth of the temporal liquid water saturation presented remarkable difference when local temperature varied. The condensate water breakthrough paths were identified. The cyclic release of condensate water droplets into the channel activated the water saturation fluctuations. Water saturation fluctuated wildly in the GDL with rib along the thickness direction, due to the role of rib in impeding the removal of water. Besides, it was noticed that the rib was not beneficial for oxygen diffusion apart from hindering the condensate water transport. A phase change solver was developed in OpenFOAM platform and validated to model the vapor condensation in a realistic structural GDL. The temporal varying condensate droplets' distributions were displayed and the droplets evolution processes were summarized. The rib was not beneficial for the oxygen diffusion apart from hindering the condensate water transport, which increases the risks of water flooding.