Particle image velocimetry (PIV) technique was used to test the gas-liquid two-phase flow field dynamics above the membrane approach in six different aeration intensity conditions. The liquid flow field above the membrane approach was tested, and the membrane surface mass transfer, thickness of concentration polarization boundary layer, shear stress and some other mass transfer parameters of membrane surface were calculated. The conclusion shows that the aeration intensity and liquid phase velocimetry strongly influence the characteristic of membrane surface mass transfer, and the aeration intensity increased in a certain range can make the membrane surface mass transfer characteristic strengthen. The paper provides experimental data and research experience for optimization design of membrane bio-reactor.