Abstract: 【Objective】 To explore the degradation of acetamiprid, carbendazim, difenoconazole and nitriconazole in muskmelon treated with Brassinolide (BR) and its mechanism. 【Methods】 Melons were treated with Brassinolide and clean water, and then sprayed with pesticides.Samples were taken at 2 h, 1 d, 3 d, 5 d, 7d, 9 d, 15 d and 24 d respectively to determine the content of pesticide residues, detoxifying enzyme activity, reactive oxygen species content, detoxifying gene expression and metabolites in the muskmelon fruit. 【Results】 Compared with the water control group, the brassinolide treatment group significantly (P<0.05) reduced the contents of acetamiprid, carbendazim, difenoconazole and nitriconazole in melon fruit, reduced the production of malonaldehyde (MDA), significantly reduced the production rate of superoxide anion (O^2-), and maintained a high detoxification enzyme catalase (CAT), peroxidase (POD) Phenylalanine ammonia lyase (PAL) and glutathione reductase (GR) activities, and the contents of soluble protein, reduced glutathione (GSH) and hydrogen peroxide (H₂O₂) were maintained at a high level.It had no significant effect on superoxide dismutase (SOD) and ascorbate peroxidase (APX).The expression of six detoxification genes increased to some extent. 【Conclusion】 Spraying brassinolide can increase the content of detoxifying substances, the activity of detoxifying enzymes, the expression of detoxifying genes and alleviate the harm caused by reactive oxygen metabolism in melon fruit, and finally reduce the content of pesticide residues in melon fruit.