Abstract: The flow fields in an ejector was mathematically formulated with realizable k-ε model and numerically simulated with Fluent software and experimentally evaluated.The influence of the axial length,exit position and divergent angle of the nozzle on performance of the ejector was investigated.The simulated results show that the entrainment behavior of the ejector strongly depends on the axial length and exit position,but little on the divergent angle of a nozzle.For example,when the contraction section is 6 times of the throat diameter and the exit position is 1.8 times of the diameter of cylindrical mixing chamber in a nozzle,the ejector exhibits the best entrainment.The simulated and measured results were in good agreement.We suggest that the simulated results be of some technological interest in design optimization of the ejector.