highlights � The performance and flow field inside ejectors are studied numerically and experimentally. � The pressures before the second shock position remain constant during the critical mode. � NXP has an optimal value for entrainment ratio, but no effect on the critical discharged pressure. abstract The present paper performs experimental and numerical investigations on the global performance and internal flow of a supersonic air ejector. The effects of operation parameters and geometrical factor on the air ejector performance have been analyzed. The results show that: the static wall pressure and axisymmetric line static pressure remain constant in critical mode under different discharged pressures, but they both increase in sub-critical mode with the increase of the discharged pressure. The shock position of the mixed fluid moves upstream in critical mode. The second shock position disappears in sub-critical mode. The experimental and numerical results indicate that there exists an optimal nozzle exit position (NXP) corresponding to maximum entrainment ratio, but the critical value of discharged pressure is almost independent of NXP.