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 internal of the expansion kettle shell is divided into a first cavity and a second cavity by a separation plate; and the kettle end cover is provided with an injecting port, a pressure cover seal, a radiator exhaust water pipe joint, an engine exhaust water pipe joint, an engine water replenishing pipe joint, a pressure relief guide pipe, an exhaust guide pipe and an internal core body. Through two cavities and one internal core body in the expansion kettle shell, and through first-grade physical absorption and isolation and two-grade and third-grade chemical effects, rust, scales and bubbles generated during working of a cooling system are absorbed, such potential threats as calcium magnesium iron ions and acid ions are reacted and treated, the pH value of cooling liquid is kept constant, and the clean and safe cleaning liquid is output to a system, so that the safe, long-time and efficient operation of the cooling system is guaranteed, the whole vehicle failure rate is reduced, and the vehicle use cost is reduced.