The utility model relates to an expansion tank technical field, in particular to expansion tank for automobile, including last box and lower box, last box be in the same place with lower box welding,one side of last box arrange pressure -releasing cover, the front end of pressure release mouth one side arrange the filling opening, the last box of pressure release mouth opposite side on be equipped with the moisturizing mouth, one side of moisturizing mouth be equipped with except that the gas port, the one side of removing the gas port be equipped with the draw -in groove, make things convenient for the assembly of level sensor joint, the rubber tube that gas port and moisturizing mouth connect that removes move towards unanimous, through inside muscle position access structure, advance an upward function under having realized. The utility model provides a beneficial effect that technical scheme brought is: through blow molding simple structure, injection structure can satisfy whole thickness requirement, realizes the front surface and arranges the filling opening, and the purpose of pressure release mouth is arranged to a high position, the design of draw -in groove makes satisfies the outside joint formula structure of sensor, with the anti -icing fluid non -contact, prevents that anti -icing fluid from revealing.