Adiabatic compressed air energy storage (A-CAES) is a promising massive energy storage to eliminate the fluctuation nature of renewable energy. In a traditional A-CAES system, a throttle valve is installed in front of air storage tank to reduce the unstable effect of pressure change in air storage tank on compression train. This study proposes a novel A-CAES system, where ejector is used to replace the throttle valve to recover pressure energy and reduce throttling loss. The charging process of the proposed A-CAES system included two periods. In the first charging period, the ejector works, and the secondary fluid of the ejector is from the outlet air of the 3rd stage compressor. In the second period, the ejector stops working and the 4-th stage compressor implements varying rotation speed operation to adapt the pressure changing in air storage tank. The mass flow rate of compression train keeps constant controlled by the regulating valve installed inlet of compression train. A dynamic model and an exergy destruction model of the proposed A-CAES system are established. The simulation results show that the ejector can improve exergy efficiency and shorten the range of unstable operation. The average exergy efficiency of proposed system increases with the increase of initial storage pressure and the optimization effect of the varying rotation speed operation on average exergy efficiency is more obvious.