An ejector aiming at an 80 kW polymer electrolyte membrane fuel cell system designed based on the Sokolov 1-D ejector mode is evaluated numerically and experimentally. A two-dimensional axisymmetric model for the ejector is established based on the Shear Stress Transport model and the Re-Normalization Group model and validated by comparing simulated results and experimental data. Effects of the ejector's mixing chamber diameter and diffusion chamber angle and humidity of the secondary flow on its performance are investigated by a Computational Fluid Dynamics method. The results show that the primary mass flow rate presents a linear relationship with the primary pressure and that the Re-Normalization Group model is more accurate than the Shear Stress Transport model in predicting the ejector's performance. When the diffusion chamber angle is 11 degrees and 13 degrees, the ejector exhibits the best performances. The mixing chamber diameter and the secondary flow humidity significantly influence entertainment ratio and hydrogen recirculation of the ejector.