Abstract: Idesia polycarpa Maxim cake meal, a significant by-product of oil processing, was systematically utilized for the first time to develop an efficient preparation technology for total flavonoids. Using Idesia polycarpa cake meal as raw material, the ultrasound-assisted extraction process was optimized via response surface methodology, followed by purification with AB-8 macroporous resin and preliminary structural characterization of the extracts through LC-MS/MS. The antioxidant activities were comprehensively evaluated, including DPPH and ABTS⁺ radical scavenging capacities as well as reducing power (FRAP).The results showed that under optimal conditions (ultrasonic power: 400 W, extraction time: 70 min, liquid-to-material ratio: 50:1 mL/g), the total flavonoid yield reached 47.85±0.05 mg/g. Purification with AB-8 macroporous resin increased flavonoid purity to 39.06%±0.99%, while LC-MS/MS analysis identified seven characteristic flavonoid components, including quercetin and quercetin-3-O-glucoside. In vitro, antioxidant assays demonstrated that purified flavonoids exhibited enhanced DPPH radical scavenging activity (IC₅₀ = 0.057 mg/mL), representing a 33.7% improvement over unpurified extracts, with a FRAP value of 13.68 mmol/L at 2 mg/mL. The study confirms that the remarkable antioxidant capacity of Idesia polycarpa Maxim cake meal flavonoids is closely related to its characteristic components, highlighting the potential for valorizing this industrial by-product.