The aim of this paper is to investigate the entrainment behavior and performance of gas-liquid ejectors. computational fluid dynamics(CFD) model and the corresponding algorithm are developed and validation experiment has been carried out over a wide range of operation conditions for ejector with different configurations. Good agreement has been achieved between the predicted values from CFD simulation and the actual data by experimental measurement. The flow patterns that occur within the primary nozzle region are analyzed on the basis of one-dimensional isentropic compressible flow theory. The fluid pairs, consisting of the motive and the entrained fluids, are considered during the investigation with N-2-H2O and He-LO2 selected as the representative fluids. The investigation results indicate that for fixed primary flow and secondary flow pressures (P-P and P-S, respectively), the entrained mass flow rate m(S) decreases linearly with the increasing pressure difference Delta P, while for fixed Delta P and secondary flow pressure P-S, the entrainment rate m(S) monotonically increases with an increase in primary flow pressure P-P until a constant value is reached. Moreover, the mixing tube length has proven to be an important design parameter and can exert a remarkable influence on ejector performance. The optimum mixing tube length of gas-liquid ejector is about 1-2 times the mixing tube diameter, and deviation from the optimum value can dramatically degrade its entrainment performance. In other words, an obvious peak value of entrainment ratio appears at the optimum L/D. However, the optimum value of L/D for single-phase ejector happens in the range of 5-7, which differs significantly from that of gas-liquid ejector. Moreover, an inapparent effect has been observed when the mixing tube of single-phase ejector is longer than the optimum value. A detailed description of this phenomenon is presented in this paper. The conclusions of the research can be served as a guideline for ejector design. (C) 2010 Elsevier Ltd. All rights reserved.