In order to transfer energy between two fluids directly and more efficiently, a novel pressure-exchange ejector was designed, and a multi-period numerical model considering leakage and gradual opening and closing of the ports was set up. The numerical model was validated by experiment and results proved that it could capture the shock wave accurately and predict the performance of pressure-exchange ejector effectively. The pressure waves in one working cycle and the flow field were displayed based on numerical simulation. Results shew that the energy was transfered by pressure waves and the vortexes generated during gradual opening and closing process led to a significant mixing between fluids and a distortion contact interface. Finally the effects of rotary speed and the gaps between ports and channels were investigated. With the increase of the inlet gap, the performance of the device reduced, while the outlet gap had a slight influence on performance. Besides, there was an optimal rotary speed for a fixed geometrical arrangement.