Generally, two flow patterns existed in membrane bio-reactor; i.e. bubbly flow and plug flow. In this study, both numerical and experimental investigations were conducted to study the hydrodynamic behavior of a two phases (water-air) membrane bio-reactor (MBR) system under these two designated flow patterns. Particle image velocimetry (PIV) was adopted for experiment and computational fluid dynamics (CFD) was chosen as the numerical tool. In order to replicate experimental observations, the CFD model integrated Eulerian multiphase model with porous medium scheme and incorporated the vertically dependent filtration flux. A steady-state simulation was conducted for bubbly flow case and a transient simulation for plug flow case. Good agreements were achieved from the comparison between experiments and simulations.