In this study, the numerical analysis and experimental measurements are conducted on the internal flow field and temperature distribution of ejectors with different throat diameters. The computational fluid dynamics (CFD) is used to simulate different ejectors and investigate the effects of Mach number, pressure, and temperature distributions. The hydrogen Entrainment Ratio (ER) of ejectors is also measured for proton exchange membrane fuel cell applications. The experimental measurements and simulations of the hydrogen Entrainment Ratio of the ejectors showed that the recovery efficiencies are 59%, 53%, and 33% for the pipe diameters of 0.5, 0.7, and 1.0 mm at the inlet pressures of 340 kPa, respectively. In different area ratios, the larger area ratio of the nozzle leads to greater difference between the diameter of the throat and the diameter of the throat outlet. This causes a smaller recovery rate. In the internal flow field of the ejector, higher recovery rate can be achieved by using the closer location of the positive shock wave to the nozzle outlet. •The ejectors with different throat diameter designs are created.•The larger the area ratio of the nozzle resulting in a smaller recovery rate.•The 0.5 mm diameter ejector has higher hydrogen recovery rate.