A vehicle thermal management system including a heating heat exchanger which exchanges heat with air within an air-conditioning case to heat the air, and a cooling heat exchanger which exchanges heat with air to cool the air; a refrigerant line circulating through a compressor, a condenser, an expansion valve, and a chiller; a first coolant line that passes through the heating heat exchanger and exchanges heat with the condenser of the refrigerant line; a second coolant line that passes through the cooling heat exchanger and exchanges heat with the chiller of the refrigerant line; a radiator that exchanges heat between the coolant and outside air; a third coolant line that passes through the radiator and exchanges heat with a battery of a vehicle; and a mixing tank provided to mix the coolant of the first coolant line, the second coolant line, and the third coolant line.