The supercritical CO2 extraction processing of flavonoids was optimized with Poacynum hendersonii leave as raw material. Firstly, the influences of the type and pH value for cosolvent were explored by single factor experiments. And the 70% ethanol with pH value of 10 was fixed as cosolvent. Then, the effects of extracting factors such as extracting pressure, temperature, time and cosolvent dosage, were investigated with orthogonal experiments. According to the researching report, the optimal process conditions were as follows: 150 g raw material, extraction temperature 45 ℃, extraction pressure 20 MPa, extraction time of 2 h, 70% ethanol with pH value of 10 as cosolvent, 900 mL cosolvent. Under these conditions, the extraction rate for flavonoids of Poacynum hendersonii could reach 5.28%, which is higher than the rate of extraction solvent extraction method.