An investigation of the gas-liquid ejector has been carried out to study the influence of operating conditions and ejector geometries on the hydrodynamics and mass transfer characteristics of the ejector by using three-dimensional CFD modeling. The CFD results were validated with experimental data. Flow field analysis and prediction of ejector performance were also conducted. Variations of the operating conditions were made by changing the gas-liquid flow rates ratio in the range of 0.2 to 1.2. The length to diameter ratio of mixing tube ($L_M/D_M$) was also varied from 4 to 10. CFD studies show that at $L_M/D_M=5.5$, the volumetric mass transfer coefficient increases with respect to gas flow rate. Meanwhile, at $L_M/D_M=4$, the plot of volumetric mass transfer coefficient to gas-liquid flow rate ratio reaches the maximum at gas-liquid flow rate ratio of 0.6. This study also shows that volumetric mass transfer coefficient decreases with the increase of mixing tube length.