The invention relates to an expansion kettle and a treatment method. The expansion kettle comprises an expansion kettle shell and a kettle end cover. The expansion kettle shell is divided into a first chamber and a second chamber. The kettle end cover is provided with a filling opening, a pressure seal cover, a radiator exhaust water pipe connector, an engine exhaust water pipe connector, an engine water supply pipe connector, a pressure relief conduit, an exhaust conduit and a built-in core. According to the technical scheme, through the two chambers in the expansion kettle shell, the built-in core, first-stage physical absorption and isolation, and second-stage and third-stage chemical action, rust, incrustation and bubbles generated in work of a cooling system are absorbed, potential threats of calcium and magnesium ions, acid irons and the like are processed through reaction, the PH value of a cooling liquid is kept constant, clean and safe cooling liquid is output for the system, and thus safe, lasting and efficient operation of the cooling system is ensured, and the whole vehicle failure rate and user vehicle usage cost are reduced.