The composition of stripping solution is V (sulfuric acid) ∶V (nitric acid) ∶V (stripping agent) =3∶ 1∶4. Among them, the deplating agent is butynediol aqueous solution, and its preparation method is as follows: 2,000 grams of butynediol is added into hot water, dissolved in 25 liters of butynediol aqueous solution, and dissolved by stirring, wherein the mass concentration of butynediol is 80 grams/liter ... When preparing deplating solution, sulfuric acid is first poured into a container, cooled with water outside the container, then nitric acid is poured, and after the temperature is lowered, the deplating agent is dripped (slowly). The deplating time depends on the coating conditions of specific products, generally 2 ~ 4 minutes.