The supersonic ejector-diffuser system has been extensively deployed in many industrial applications due to its exclusive advantages such as no moving parts and structural simplicity compared to other fluid machineries. However, the conventional single-stage ejector-diffuser system has been criticized for its inefficiency because of the energy loss during the mixing process and primarily, the momentum waste during the discharging process. The introduction of a two-stage ejector-diffuser system can be a useful configuration to utilize the redundant momentum of the discharged flow for improving the system performance. In the present study, the flow phenomena inside single-stage and two-stage ejector-diffuser systems have been critically predicted by means of the numerical approach using Reynolds averaged Navier-Stokes equations and the theoretical evaluation using 1D mathematical model. Both numerical and theoretical results were validated with existing experimental data. Detailed explanation and comparison has been given to detect the performance of two-stage ejector and single-stage ejector. Essential benefit coefficients obtained in the present study were specified in terms of entrainment ratio, mass flow flux ratio and the coefficient of power (COPR). Primary results of the two-stage ejector-diffuser system showed favorable capacity of collecting the extra momentum and increasing the entrainment effects of the system. (C) 2015 Elsevier Ltd. All rights reserved.