Abstract: Based on walnut diaphragm as the raw material, processing conditions for the ultrahigh pressure extraction of total flavonoids from walnut diaphragm using response surface methodology ( RSM) were optimized. Meanwhile, a kinetics model was developed.The major factors included alcohol concentration, pressure, pressure holding time and solid-liquid ratio, Box-Benhnken experimental design was utilized to investigated the influence of different factors and their interactions on the extraction rate of total flavonoids. Also, kinetic equation of extracting total flavonoids under ultrahigh pressure was developed according to Fick 's first law of diffusion. The results indicated that 62%, 385 MPa, 9 min, and 1 ∶ 25 were the optimum extraction parameters for ethanol concentration, extraction pressure, pressure holding time and solid-liquid ratio, respectively.Under such conditions, the actual extraction rate of total flavonoids was 12.31%, which was consistent with the predicted values.The predicted value of kinetic model was well correlated with the actual value, and the coefficient of determination R2 was 0.9875. Compared with the traditional heating method, the ultrahigh pressure extraction process can significantly increase the extraction rate and shorten the extraction time.