A thermal management system may include a battery line connected to a high-voltage battery core and having a first radiator, and through which cooling water flows by a first pump; an introduction line having an end connected to an upstream side of the first radiator and the other end connected to the internal air-conditioning heating core, and through which cooling water flows by a second pump; a discharge line having an end connected to an upstream side of the high-voltage battery core in the battery line and the other end connected to the internal air-conditioning heating core, and through which the cooling water introduced through the introduction line flows; a refrigerant line having an expansion valve, an internal air-conditioning cooling core, a compressor, and an air-cooling condenser and through which a refrigerant flows; and a water-cooling condenser connecting the refrigerant line and the introduction line.