Abstract: To explore the influence of the protein mass volume percentage concentration (hereinafter referred to as the concentration) in the ultrasound system on the modification effect, in this paper, different concentrations of peanut protein were prepared and ultrasonic treatment was conducted. The subunit composition, surface hydrophobicity, endogenous fluorescence emission wavelength, secondary structure and molecular weight of peanut proteins were analyzed by SDS-PAGE, fluorescence spectrum, Fourier transform infrared spectrum and high performance liquid chromatography, respectively. Through the above structural analysis, it was found that the composition and the primary structure of peanut protein was not changed by ultrasonic treatment. After ultrasonic treatment (400 W, 5 min), the surface hydrophobicity and exposed sulfhydryl group content of peanut protein with a higher concentration (0.1 g/mL) were significantly increased, the wavelength of endogenous fluorescence emission was redshifted obviously, and the average particle size increased the most, but the particle size decreased with the increase of ultrasonic intensity. By high performance liquid chromatography (HPLC) determination, it was found that after ultrasonic processing, large molecular weight protein was formed, besides, peanut protein also contained a few lower molecular weight components, indicating that peanut protein subunits were aggregated and a small amount of protein subunits from original oligomers dissociated. The content of disulfide bond was the highest in peanut protein with a lower concentration (0.01 g/mL) after ultrasonic treatment, and the secondary structure changed significantly, showing that the content of β-sheet significantly decreased, and the content of β-turn significantly increased. Therefore, in order to achieve a desired modification target of a molecular structure, it is very important to select an appropriate protein concentration during ultrasound.