The present invention relates to an air-conditioner system for a vehicle and a method for controlling the same, and more particularly, relates to an air-conditioner system for a vehicle and a method for controlling the same, which changes a target heat degree according to variation in an amount of refrigerant discharged from a compressor, or in other words, gradually decreases the target heat degree as the amount of refrigerant discharged from the compressor decreases, and controls an electronic expansion valve on the basis of the gradually-decreased target heat degree, thereby restraining a change in a heating degree in a region where the amount of refrigerant discharged from the compressor varies, and thus preventing degradation of an air conditioner and stabilizing the system.