The invention provides a Fenton and Fenton-like system fortifier and a using method thereof, which relate to a water treating fortifier and a using method thereof and overcomes the defects that the pH value of the Fenton and Fenton-like system reaction water body is limited, the adding amount of Fe<2+> is overhigh in the Fenton reaction, and the reaction speed is low in Fenton-like reaction. The fortifier is selected from ascorbic acid, sodium sulfite, lithium sulfite, potassium sulfite, magnesium sulfite, calcium sulfite, hydroxylamine, hydroxyl-ammonium perchlorate, hydroxylamine sulfate, hydrazine, N,N-diethylhydroxylamine, carbohydrazide, ethanolamine, a hydroxylamine solution or N,N,N',N'-tetra substituted phenylenediamines. The using method has the following steps of: adding the Fenton and Fenton-like system fortifier, fortificated chemicals and peroxide into the treated water body; and then, uniformly stirring to react. The fortifier can accelerate the reaction of water treatment and decrease the using amount of the fortificated chemicals.