Heat pump system for vehicle

A heat pump system for a vehicle, which includes a dehumidification line R4 for supplying some of refrigerant circulating a refrigerant circulation line R to an evaporator 160 before the refrigerant is introduced into an exterior heat exchanger 130 after passing a first expansion means 120 so as to dehumidify the interior of the vehicle in a heat pump mode, thereby allowing the refrigerant to smoothly flow to the evaporator 160 of a low pressure through the dehumidification line before the refrigerant is introduced into the exterior heat exchanger 130 which has a higher pressure than the evaporator when the interior of the vehicle is dehumidified, and smoothly dehumidifying the inside of the vehicle.