The compressed air energy storage (CAES) system generally adopts compressors and turbines to operate under a constant pressure ratio. The system working parameters cannot adapt to load change, which causes the system efficiency to be limited. In order to improve CAES system efficiency, a novel variable pressure ratio CAES system is proposed to change the operation pressure ratio by controlling the opening or closing of valves between compressors and the opening or closing of valves between turbines. The thermodynamic analysis model of variable pressure ratio CAES system is established. The period of energy storage, the power consumption of compressor, the output work of turbine and the charging and discharging efficiency of system are calculated and analyzed for the 500 kW advanced adiabatic CAES system. The results show that compared with the corresponding constant pressure ratio CAES system, in the variable pressure ratio CAES system, the power consumption of compressor is reduced by 12%, the output work of turbine is increased by 17.9% and the charging and discharging efficiency of system is increased by 13.1%. Therefore, variable pressure ratio CAES system can not only significantly improve its energy storage efficiency, but also be easy to realize. (C) 2018 Elsevier Ltd. All rights reserved.