Abstract: Numerical investigation was conducted in which ejecting mode of a multi-cycle pulsed detonation rocket engine with a simple cylindrical ejector was simulated using unsteady axisymmetric N-S Eqs.Experiments were carried out to measure the ejection ratio,which was used as the comparative parameter.The result of simulation is in good agreement with that of experiment.Ejecting process was divided into three phases corresponding to three different working mechanisms:(1) air compression and acceleration by shockwave;(2) shearing and dragging of the plume;(3) action of inertia and pressure gradients.The simulation result can also be used as a reference for the design of fuel injection.