Choose lye as extraction solvent, protein from seed of Trichosanthes kirilowii Maxim was extracted by ultrasonic technology. The optimal ultrasonic-assisted extraction technology was determined by single factor experiment and orthogonalexperiment. Meanwhile，antioxidant activity of protein t on DPPH free radical and hydroxyl radical was evaluated. Results showed: the optimal ultrasonic-assisted extraction technology of protein in seed of Trichosanthes kirilowii Maxim was: lye as extraction solvent of pH 10 including 0.7 mol/L NaCl, material-to-liquid ratio of 1:30 (g:mL), ultrasonic power of 200 W , ultrasonic-assisted extracting time about 30 min and extraction temperature at 70℃. The extraction rate of protein reached about 22% with the optimal ultrasonic-assisted extraction technology. When the protein concentrationt was 0.8 mg/mL, the scavening rate on DPPH free radical and the scavening rate on hydroxyl radical were 66.46%, 49.23% respectively.The scavenge capability of DPPH free radical and hydroxyl radical increased along with the increase of the protein concentrationt, it was superior to citric acid but inferior to ascorbic acid.