Abstract: Compressed air energy storage also has shortcomings of low energy storage efficiency and long payback period. At present,most compressed air energy storage systems use adiabatic compression. When the compressed air is compressed,a large amount of power is consumed into heat. In this paper,a method was proposed,using the isothermal piston to absorb the heat in the compressed air and discharge the heat to the liquid at the bottom of the cylinder. Firstly,a dimensionless mathematical model of isothermal piston cooling was established. Then the dimensionless coefficients K_a and X_u affecting the heat transfer of isothermal piston were proposed and its influence on the isothermal piston compression system was analyzed. Finally,an example calculation was made with aluminum foam to form an isothermal piston,compression ratio of 7,speed 1 200 r/min,compression efficiency can be increased 11%.