The　Compressed　Air　Energy　Storage　(CAES)　system　is　a　promising　energy　storage　technology　that　has　the　advantages　of　low　investment　cost,　high　safety,　long　life,　and　is　clean　and　non-polluting.　The　compressor/expander　is　the　core　equipment　of　the　CAES　system,　and　its　performance　has　a　decisive　impact　on　the　overall　system　efficiency　and　economic　performance.　Based　on　the　pneumatic　motor,　this　study　proposes　and　designs　a　test　bench　of　the　CAES　system　that　integrates　compression　and　expansion　functions.　The　off-design　operation　condition　represented　by　the　pressure　change　in　the　air　tank　has　an　important　influence　on　the　efficiency　and　economy　of　the　CAES　system.　The　effect　of　key　parameters　such　as　air　tank　pressure,　torque,　and　mass　flow　rate　on　the　output　and　efficiency　of　the　compressor　is　investigated.　When　the　CAES　system　is　operating　in　energy　storage　mode,　the　compressor　must　continuously　deliver　gas　to　the　gas　storage.　The　working　pressure　of　the　compressor　increases　with　the　pressure　in　the　air　tank,　so　the　compressor　used　for　energy　storage　must　operate　continuously　over　a　wide　range　of　working　conditions.　The　parallel　operation　mode　of　the　compressor　is　proposed　to　improve　the　working　condition　range　of　the　compressor　torque　and　current,　and　improve　the　isotropic　efficiency.　When　the　air　receiver　pressure　is　2.6　bar　and　the　rotational　speed　is　2850　r/min,　the　power　consumption　of　the　compressor　reaches　the　maximum　value　of　approximately　1233.1　W.　This　new　parallel　mode　could　provide　a　CAES　unit　a　systematic　solution.　©　2023　by　the　authors.