Abstract: The flavonoid was extracted from Citrus reticulata Blanco using ultrasonic extraction technique, and the antioxidant activities of them were tested by 1,1-diphenyl-2-picrylhydrazyl（DPPH） assay and 2,2’-azino-bis3-ethylbenzothiazoline-6-sulfonic acid（ABTS） assay. The effects of ethanol concertration, ultrasonic extraction time and the solid-liquid ratio on the extraction of flavonoids from Pericarpium citri reticulatae were studied by response surface design method. The optimum extraction conditions were obtained as follows: the mass faction of ethanol was 60%, ultrasonic extraction time was 36 minute, solid-liquid ratio was 1 ∶25（g/mL）. Under the above conditions the extraction rate of flavonoids was 24.75 mg/g. The DPPH assay showed that the IC50 values of flavonoids from PCR before purification and after purification by ethyl acetate and AB-8 resin were 427.83,129.76 and 87.44 μg/mL and the ascorbic acid equivalent（AEAC） values of them were 1 283.85, 4 266.04 and 6245.73 mg/100 g. The ABTS assay showed that the IC50 values of them were 181.67, 50.87 and 43.3 μg/mL and the AEAC values were 8 584.79, 30 690.99 and 36 006.24 mg/100 g. The antioxidant activities of flavonoids from PCR had a dose-effect relationship and would be stronger after purification.