Abstract: The numerical study on the performance of a double flow-pass tube-fin heat exchanger was performed with different air and refrigerant inlet parameters. An optimization design of circuit arrangement was presented and was validated by the numerical simulation results. The results showed that there was an optimal ratio between the two flow-pass tube diameters in the heat exchangers. In this paper the optimal ratio was 0.8 and with this optimal ratio，the heat transfer performance of the heat exchanger could be enhanced by 6%~11%，at the same time the pressure drop of the air side could be decreased by 2%.