The invention provides an anti-oxidation detergent composition, a diesel oil composition and a method for improving the anti-oxidation property and cleaning property of diesel oil. The anti-oxidation detergent composition comprises an antioxidant and Mannich base, wherein the antioxidant is an arylamine type antioxidant and/or a hindered phenol type antioxidant; the Mannich base comprises the structural unit (I) and structural unit (II) shown in the specification, wherein each R1 is independently selected from hydrogen, a C1-C4 straight chain or branch-chain alkyl and a single bond; each R' is selected from a C1-C6 straight chain or branch chain alkyl; R4 is selected from hydrocarbyl of which the number-average molecular weight Mn is 300 to 3000; each y is independently selected from an integer from 2 to 5. The anti-oxidation detergent composition and the diesel oil composition disclosed by the invention are excellent in anti-oxidation property and cleaning property and can be used for inhibiting generation of precipitates in an engine.