Expansion tank for car use, including the main expansion tank, expansion tank, Lord, vice respectively by gas liquid expansion tank, cooling fluid connect piping connections, gas liquid line, cooling fluid respectively extend to the end of line pair of expansion tank below the surface of cooling liquid, gas and liquid line, cooling fluid piping are arranged separately first, two one-way valve, the first check valve conduction direction by the main expansion tank to pair of bentonite The direction of the second check valve flows from the auxiliary expansion box to the main expansion box. The expansion box of the above structure has the advantages of simple structure, low production cost, and can effectively recover the spilled cooling liquid and steam mixture and reverse replenish the cooling liquid back to the main expansion box under atmospheric pressure.