Abstract: The radial and axial gas holdups in the inner loop of an airlift reactor with a down tube and an annulus gas distributor are investigated under different superficial gas and external liquid circulation velocities. Experimental installation is made of plexiglass with an inner diameter of 0.284m and a height of 3.0m. Air and tap water were used as the gas and liquid phase, respectively. The experimental results show that the radial gas holdup within the inner loop increases with an increase of superficial gas or external liquid circulation velocity. These distribution characteristics at different axial locations are influenced obviously by the reactor structure. The axial profile of the sectionaveraged gas holdup firstly increases with axial height increasing, and then decreases slightly above the exit of the draft tube. Furthermore, the distributions of gas holdup are numerically computed by using an ANSYS CFX10.0 software package. The computational results indicate that the radial distributions of gas holdup are nonaxial symmetry in nature, which is caused by the nonaxial symmetry of the setup. The axial gas holdup increases dramatically above the gas distributor. There exists a minimal gas holdup below the exit of the down tube, which is resulted from the external liquid. The simulated data aforesaid can provide additional information for the experimental investigation. Therefore, it is suggested that the method combining experiment with simulation is suitable for the development of a new type of multiphase reactor.