In recent years, xEVs (including BEVs, HEVs, PHEVs, and FCEVs) have rapidly spread across the globe in an effort to meet stricter environmental regulations. Under such circumstances, it is required to reduce the amount of power used for air conditioning, which directly affects their driving range. For the heat pump systems of xEVs that can reduce the power consumption of air conditioning in winter, we made computational models of the air conditioning cycle and its control system, and through simulation studied the control of heat pump systems to achieve both power saving and thermal comfort.Subsequently, we also confirmed that both high efficiency and thermal comfort can be achieved by controlling the components of the heat pump system properly with vehicle test.