To optimize the microwave-assisted ethanol extraction of Astragali Radix flavonoids and evaluate their antioxidant activity in vitro, a central composite design response surface methodology was employed. Extraction temperature, time, liquid-to-solid ratio, and ethanol concentration were selected as independent variables, with flavonoid yield as the response value. The antioxidant activity in vitro was assessed using DPPH, ABTS⁺, and OH⁻ radicals scavenging assays. The results demonstrated that the optimal extraction parameters were as follows: temperature of 102 ℃, time of 25 min, liquid-to-solid ratio of 24∶1 (mL/g), and ethanol concentration of 87%. Under these optimized conditions, the flavonoid yield was determined to be 15.80 ± 0.03 mg/g. The scavenging abilities of Astragali Radix flavonoids on DPPH and ABTS⁺ radicals were concentration-dependent, reaching 90.11% and 89.06%, respectively, at 0.4 mg/mL, with no significant difference compared to vitamin C (P > 0.05). However, their OH⁻ radicals scavenging rate was significantly lower than that of Vitamin C (P < 0.01). The IC₅₀ values for DPPH, ABTS⁺, and OH⁻ radicals scavenging was 0.193 ± 0.021, 0.051 ± 0.017, 0.126 ± 0.008 mg/mL, respectively. Therefore, Astragali Radix flavonoids extracted using the microwave-assisted ethanol method demonstrate significant antioxidant activity in vitro.