With the global emphasis on environmental protection, new energy vehicles have become the direction of development in the automotive industry. Nowadays, the higher NVH performance from their cars is demanded. Customers feedback that there is some kind of buzzing or flowing water sound, When the air conditioning system of a new energy vehicle was turned on and off, which seriously affects the comfort of drivers and passengers. However, there is little research and explanation on this issue for new energy vehicle. This article focuses on the characteristics and mechanisms of refrigerant flow sound in the air conditioning system of new energy vehicles. Through the investigation and analysis of refrigerant flow sound in the entire vehicle air conditioning system, the noise characteristics, formation mechanism, and transmission path of refrigerant flow sound are clarified. Based on the mechanism analysis, two optimization points for controlling refrigerant flow fluctuations and refrigerant pressure pulsation transmission are summarized. The optimization plan is implemented and verified to be effective, providing a basis for the optimization of new energy vehicle air conditioning systems.