Abstract: Peanut protein was modified by acidic deamination through degree of deamination, degree of hydrolysis and the rate of two degrees as evaluation indexes. Based on results of single factor experiments, concentration of sulfuric acid, reaction time and reaction temperature were optimized by orthogonal experiment. Moreover, the composition of amino acid, secondary structure, microstructure and solubility of modified peanut protein were analyzed. Results showed that the optimal conditions were 0.30 mol/L sulfuric acid, peanut protein concentration of 5.5%, reaction temperature of 85℃, 2 h reaction time, the degree of deamination, degree of hydrolysis and the rate of two degrees reached 66.98%±0.54%, 10.56%±0.27% and 6.34, respectively. Although the primary structure and secondary structure of peanut protein kept basically stable during acidic deamination, the morphology of protein aggregates changed, and the solubility of modified peanut protein improved notably.