A heat pump system for a vehicle includes an air conditioner circulating a refrigerant through a refrigerant line, a coolant circulation device circulating a coolant through a coolant line, a first chiller connected to the coolant circulation device through the coolant line, connected to the refrigerant line through a first refrigerant connection line, and heat-exchanges a selectively introduced coolant with a refrigerant supplied from the air conditioner to control a temperature of a coolant, and a second chiller connected to the coolant circulation device through the coolant line, connected to a second refrigerant connection line so that a refrigerant is supplied from the air conditioner, and increases a temperature of a refrigerant by heat-exchanging a coolant and a refrigerant so that waste heat is recovered from a coolant selectively flowing thereinto, wherein the air conditioner includes a gas injection part that bypasses some of a refrigerant passing through a condenser to a compressor to increase a flow rate of a refrigerant circulating in the refrigerant line.