Abstract: When the electric vehicle heat pump system is heating in winter while the external environment is low temperature and high humidity, the external evaporator is easy to frost. In view of this, this paper conducts an experimental study on the frosting of the electric vehicle heat pump system in climatic wind tunnel, a comparative experiment research method is used to study the defrosting performance of heat pumps under different temperatures and humidities. The experimental results show that, under the same high humidity environment with different temperatures, the outer evaporator frosts quickly, and the COP of the heat pump system decreases gradually after frosting, and the lowest COP is only about 1.2. In the same temperature environment with different humidity, the low humidity condition (below 60%) does not frost, while the high humidity condition is easy to frost, and the total power of the frost condition is about 200W higher than that of the non-frost condition, and the COP is about 0.5 lower. When the difference between the evaporation temperature and the dew point temperature is within −10 ℃, and frosting is not likely to occur. At the same time, the cooling fan should be turned on to increase the heat exchange capacity of the external evaporator and enhance the COP of the heat pump system.