Abstract: The aim of this study was to prepare the quinoa bran protein（QBP） by the ultrasound-assisted alkaline solution-acid precipitation method, and to investigate the effects of ultrasound-assisted extraction on the structure and functional properties of QBP. Based on single factor experiment, Box-Behnken response surface methodology was used to analyze and optimize the preparation process of QBP. The changes of functional properties of QBP, such as solubility, water retention, and foaming properties, and the differences of protein molecular weight and microstructure before and after ultrasound were compared. The results show that the optimal extraction process of QBP is as follows: ultrasonic power is 400 W, ultrasonic time is 26 min, temperature is 46 ℃, pH is 10, solid-liquid ratio is 1∶22, the purity is 80.74%. Compared with conventional alkali extraction, the extraction rate of QBP is increased by 5.51%. QBP is rich in amino acids, the proportion of hydrophobic amino acids accounts for more than 1/3 of the total amino acids. The molecular weight is observed in the range from 10.0 kDa to 66.0 kDa by gel imaging system. The subunit distribution of ultrasound-assisted extraction of QBP does not change significantly, but the functional properties are improved, the particle size is reduced and more spherical small particle structures appears. This indicates that ultrasound-assisted can improve the structural and functional characteristics of QBP. This study provides theoretical support for the application of ultrasonic technology in the further processing and utilization of quinoa bran, and has reference value to the comprehensive utilization of food industrial waste resources.