Subway train air conditioning units consume approximately 40% of train traction power. Reasonable and effective increase of energy efficiency ratio (COP) of train air conditioning units is an important issue to reduce the energy consumption of subways. The paper proposes the idea of applying elliptical tube heat exchangers to the air conditioning of subway trains. By establishing a simulation model, a comparison is made between the original design using a heat exchanger with a circular tube heat exchanger and the refrigeration system with an oval tube heat exchanger. The results show that the COP of the refrigeration system is increased by 12.4% and the refrigeration capacity is increased by 12.6% after both condenser and evaporator are optimized with elliptical tubes. Smaller compressors can be selected to further reduce costs. In addition, an analysis of the refrigeration system optimized for enhanced tube evaporators was conducted. The results show that the performance of the refrigeration system using the enhanced tube evaporator has also improved, which is slightly inferior to that of the elliptical tube evaporator. Therefore, the elliptical tube heat exchanger is applied to the subway train air conditioning unit, and the performance of the refrigeration system is significantly improved, which is of great significance for reducing the energy consumption of the subway train.