Abstract: The GWP value of R134a refrigerant is high, and the refrigerant will be eliminated in the future. However, it is not clear that what kind of refrigerant would replace R134a. In view of this, this paper puts forward that using ammonia as alternative refrigerant of R134a, and applies this to the electric vehicle air conditioning system. At the same time, we conducted a performance research for ammonia working medium electric vehicle air conditioning system. The research result shows that the theoretical COP of ammonia working medium electric vehicle air conditioning system increases with the increase of evaporation temperature and super cooling degree, decreases with the increase of condensation temperature and superheat degree. The theoretical COP of ammonia working medium of electric vehicle air conditioning system is 4.09, which is equivalent to the R1234yf theory COP. However, As for the improved system, Ammonia is more safe and reliable than R1234yf. Compared to R152a, ammonia GWP is lower, and has a better environmental performance. Compared to CO2, ammonia COP is higher andmore energy can be saved.