An air-conditioning system includes a humidifier, a dehumidifier, transfer fans for transferring air of an air-conditioned room to a room, a damper for independently controlling an air volume transferred to the room, a system controller for controlling the humidifier, the dehumidifier and the damper, a room humidity sensor and an air-conditioned room humidity sensor. The system controller further includes an air-conditioned room humidity controller for maintaining the humidity of the air-conditioned room within a specified humidity range defined by a minimum humidity and a maximum humidity, an air volume determiner for determining an air volume passing through the damper according to the humidity of the room obtained by the room humidity sensor and the humidity of the air-conditioned room obtained by the air-conditioned room humidity sensor and a damper controller for controlling the air volume transferred to the room passing through the damper.