In this study, the round trip efficiency of a multistage adiabatic compressed air energy storage (A-CAES) system was optimized by differential evolution (DE) algorithm, and decision variables were the pressure ratio of each compressor/expander. The variation of the pressure ratio of each compressor/expander leads to different inlet air temperatures of the heat exchanger. Thus, this optimization method provides more heat energy recovery from compression to increase the inlet air temperature of expanders. Results indicate that the optimization method is effective for the pressure ratio allocation, improving the system efficiency by ∼1% and exergy efficiency of the heat storage process by 5.3% to the maximum compared with an equal pressure ratio distribution A-CAES system. Besides, a uniformity factor of temperature difference (UFTD) of multistage heat exchangers is proposed to analyze the temperature uniformity of the multistage heat exchangers, which indicates that decreasing the UFTD contributes to an increased uniformity of the temperature field and an improvement in heat transfer efficiency. The study is extended onto optimal off-design system configuration and the recommendations are proposed, which provides a guidance for A-CAES system design.