Objective To optimize the extraction process of flavonoids from Xinyang Camellia sinensis and to compare the in vitro antioxidant activities of total flavonoids before and after purification.Methods Using Xinyang C. sinensis as raw material, a one-factor test is conducted to investigate the effects of ethanol volume fraction, ultrasonic time, ultrasonic power, and material-liquid ratio on the yield of flavonoids. Subsequently, a three-factor, three-level optimization model is established based on the Box-Behnken experimental design. Additionally, a macroporous adsorption resin is utilized for the purification of flavonoid crude extracts. Finally, the in vitro antioxidant activity of the total flavonoids is evaluated by detecting their DPPH and hydroxyl free radical scavenging rates before and after purification.Results The optimized extraction conditions are: an ultrasonic time of 61 min, an ethanol volume fraction of 62%, and a solid-liquid ratio of 1∶19 (g/mL). Under these conditions, the extract yield is 9.63 mg/g, which is close to the predicted value (9.59 mg/g). Before purification, the highest DPPH and hydroxyl free radical scavenging rates by C. sinensis flavonoids are 87.21% and 55.81%, respectively; after purification, these rates are enhanced to 97.10% and 60.97%, respectively. The optimized extraction process results in an extract yield of Xinyang C. sinensis flavonoids at 9.63 mg/g, alongside significantly elevated DPPH and hydroxyl free radical scavenging ability after purification, indicating effectively enhanced in vitro antioxidant activities.Conclusion Ultrasonic-assisted extraction combined with macroporous adsorbent resin purification can significantly enhance the free radical scavenging ability of Xinyang C. sinensis flavonoids while attaining a relatively high yield.