A thermal management system for a vehicle is provided, which includes a battery line connected to a high-voltage battery core, provided with a first radiator, and configured to make cooling water flow therein by a first pump; an indoor heating line connected to a heating core for indoor air conditioning, and provided with a water heating heater therein and a second pump to make cooling water flow therein; a first battery heating line and a second battery heating line branched from a first valve provided at a downstream point of the heating core of the indoor heating line and connected to upstream and downstream points of the high-voltage battery core of the battery line, respectively; and a refrigerant line provided with an expansion valve, a cooling core for indoor air conditioning, a compressor, and an air-cooled condenser.