The present invention belongs to the field of pure copper or copper alloy cleaning, and relates to an acid washing liquid obtained by adding other substances to a sulfuric acid solution to compound and having a passivation effect. According to the present invention, contaminated pure copper or copper alloy is washed, such that the pure copper or copper alloy restores the metal luster, is not damaged, and form a layer of a dense passivation film on the surface of the pure copper or copper alloy so as to maintain brightness and beautiful look and so as not to produce darkening after being stored for a long time; and the acid mist is less so as to easily achieve environmental protection and operator body health, the acid washing amount is high, and the acid treatment cost is low.