Abstract: Aiming at energy saving and energy consumption reduction, based on the new generation B type metro train project, the power supply mode of rail transit vehicle air conditioning is optimized by adopting DC 1500 V direct frequency conversion air conditioning，which is compared with traditional air conditioning in respects of vehicle weight reduction and energy saving. The result shows that the installation of DC 1500 V direct frequency conversion air conditioning could reduce air conditioning unit weight, energy consumption and vehicle life circle cost, therefore has better economic and social benefits.