Heat and mass transfer problem in a fixed-bed tubular reactor is one of the major concerns in the chemical engineering. The two dimensional axial plug flow model was used for a water gas shift reactor to compare heat conduction or mass diffusion with convective effect. In the case of fast fluid flow in highly permeable catalyst-bed, convective heat transfer was dominant compared to heat conduction. Meanwhile both conductive mass transfer and mass diffusion were effective in mass transfer. Permeability had a large impact on homogeneity of fluid. A two dimensional particle-scale model was also investigated for detailed flow behavior. Mass distribution showed effective mixing of gas along radial direction due to high diffisivity of the gas, even when a low permeable and low porous catalyst particle was assumed.