Abstract: Based on the results of the single factor experiments, Box-Behnken ( BB) design and response surface analysis was applied to investigate the effects of pH, ultrasound time, solid-liquid rate, NaCl concentration on extraction yield of Sophora japonica L seed pretein. The quadratic term model of the protein extraction technology was established.Meanwhile, the antioxidant activity of protein on DPPH and ABTS free radical was evaluated. The results showed that the optimal extraction conditions of Sophora japonica L seed pretein were as follows: phosphate buffer with pH8.2 and containing 0.8 mol/L NaCl, ratio of liquid to solid of 31 mL/g, ultrasonic extraction time of about 29 min.Under this condition, the predicted extraction yield of protein from Sophora japonica L. was 139.36 mg/g with a relative error of 0.08% when compared with the actual yield ( 139.25 mg/g) which proved the accuracy of the results.When the protein mass concentration was 38.044 μg/mL, the scavenging rate on DPPH and ABTS free radical were 29.44% and 90.82% respectively. Sophora japonica L. abundantly contained seed proteins and the proteins had excellent free radical scavenging activity thus providing a good natural free radical scavenger.