Abstract: The air conditioning system of the Electric Multiple Units (EMU) operates for a long time and is closely related to the external environment, the system reliability is greatly affected by the operating environment. In order to study its operational reliability under the influence of environmental factors, this paper determined the main environmental factors through grey correlation analysis, and introduced environmental factors to model the operation reliability on the basis of the inherent reliability of the air conditioning system, based on the statistical analysis of the fault data of CRH380B EMU air conditioning system and the environmental monitoring data in the operation area. And based on the calculation of environmental factors through the environmental hazard matrix, this paper obtained the reliability curve of air conditioning system under the influence of environmental factors, which provided a reference for the modeling and life prediction of EMU air conditioning system under complex environment.