This paper describes a new approach to improve compressor efficiency by using 1D CAE and 3D CAE. First, a 1D simulation model of a reciprocating compressor is proposed and the compressor efficiency is analyzed. Then, heat flow in the compressor is analyzed using a 1D thermal network simulation model and the heat receiving process of the refrigerant gas is investigated. Next, gas flow in the compressor is evaluated using 3D CFD and an improved compressor with a new structure is proposed. Finally, the effect of the improved compressor is evaluated through experiments. Results demonstrated that the proposed approach is very effective in actual development.