A heat pump system for a vehicle, the heat pump system comprising: a cooling apparatus including a radiator, a first pump, a first valve, a second valve, and a reservoir tank which are connected through a coolant line, to circulate a coolant in the coolant line to cool at least one electrical component provided in the coolant line; a battery cooling apparatus including a battery coolant line connected to the coolant line through the first valve, and a second pump and a battery module which are connected through the battery coolant line to circulate the coolant in the battery module; a heating apparatus including a heating line connected to the coolant line through the second valve to heat a vehicle interior by use of a coolant and a third pump and a heater provided on the heating line; and a chiller provided in the battery coolant line between the first valve and the battery module, and connected to a refrigerant line of an air conditioner through a refrigerant connection line, to adjust a temperature of the coolant by performing heat exchange between the coolant which is circulated in the battery coolant line and a refrigerant which is selectively supplied from the air conditioner; characterized in that the chiller is connected to a chiller connection line, wherein a first end portion of the chiller connection line is connected to the coolant line through a third valve provided in the coolant line between the radiator and the second valve and a second end portion of the chiller connection line is connected to the chiller, and and in that the reservoir tank is provided in the coolant line between the radiator and the first valve, and is connected to the coolant line connecting the first valve and the first pump through a supply line bypassing the first valve. a cooling apparatus including a radiator, a first pump, a first valve, a second valve, and a reservoir tank which are connected through a coolant line, to circulate a coolant in the coolant line to cool at least one electrical component provided in the coolant line; a battery cooling apparatus including a battery coolant line connected to the coolant line through the first valve, and a second pump and a battery module which are connected through the battery coolant line to circulate the coolant in the battery module; a heating apparatus including a heating line connected to the coolant line through the second valve to heat a vehicle interior by use of a coolant and a third pump and a heater provided on the heating line; and a chiller provided in the battery coolant line between the first valve and the battery module, and connected to a refrigerant line of an air conditioner through a refrigerant connection line, to adjust a temperature of the coolant by performing heat exchange between the coolant which is circulated in the battery coolant line and a refrigerant which is selectively supplied from the air conditioner; characterized in that the chiller is connected to a chiller connection line, wherein a first end portion of the chiller connection line is connected to the coolant line through a third valve provided in the coolant line between the radiator and the second valve and a second end portion of the chiller connection line is connected to the chiller, and and in that the reservoir tank is provided in the coolant line between the radiator and the first valve, and is connected to the coolant line connecting the first valve and the first pump through a supply line bypassing the first valve.