How to reduce peanut allergies has always been a main food safety concern. Plant polyphenol complex peanut sensitizing protein was proposed as a new desensitization strategy. Gallic acid (GA), as a natural plant polyphenol, has anti-inflammatory and immunomodulatory effects. Therefore, the aim of this study was to investigate the effect of GA on peanut protein (PP) sensitization under high moisture extrusion conditions. The contents of free sulfhydryl groups and disulfide bonds in the PP-GA complex were determined, and the structure of the complex was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared spectroscopy. The results showed that with increasing GA content, the number of free sulfhydryl groups increased while the number of disulfide bonds decreased. The secondary structure of PP-GA showed that the random coils and β-turns were transformed to α -helices and β-sheets. A BALB/c mouse model was also established, wherein Al(OH)3 was used as an adjuvant when the complex was administered via intraperitoneal injection, and the mice showed mild allergic symptoms and a decreased immune organ index. In addition, the serum levels of specific antibodies (immunoglobulin E (IgE), immunoglobulin G1 (IgG1), and immunoglobulin G2a (IgG2a)), cytokines (interleukin-5 (IL-5), interleukin- 13 (IL-13), and interferon gamma (IFN-γ)) and histamine were reduced. In summary, this study proved that GA can relieve the sensitization of PP induced by high moisture extrusion.