It is important to investigate the two-phase condition in PEFC gas diffusion layer (GDL). In this study, the simulated GDL structures, such as carbon paper and carbon cloth, were developed by numerical analysis including the random orientation of carbon fibers and binders. And detailed structural estimation was carried out. Pore size distribution, electrical resistivity and tortuosity were calculated, and these values almost agreed with actual measurement values. Furthermore, in order to calculated two-phase condition in GDL, 3D pore network model based on an actual heterogeneous structure was developed by improving our past networking method. And the accumulating liquid water condition and the O2 gas diffusion performance of each GDL structure were compared on the water permeable condition. As the results, the relative diffusion coefficient models between wet and dry condition of each GDL were obtained by these calculations.