As a non-thermal technology, high-energy electron rays can effectively reduce pathogenic bacteria and mycotoxins in food. This study investigated the degradation effect of high-energy electron rays on four aflatoxins in artificially contaminated cold-pressed and hot-pressed groundnut cake. We also evaluated the irradiated groundnut cake's quality (including crude protein, amino acid, etc.). The results showed that the irradiation dose, and moisture content positively affected the degradation of aflatoxins, while the initial content of aflatoxins was detrimental to the degradation. The degradation process of aflatoxins could be better characterized by the second-order kinetics (R2 ranges 0.7162–0.9918) than first-order kinetics. The changes in the crude protein of groundnut cake by high-energy electron rays were small (all less than 3%). Still, there were some changes in the amino acid content of groundnut cake (less than 5% change in total amino acids in cold-pressed groundnut cake and no more than 8% change in total amino acids in hot-pressed groundnut cake). It was suggested that at the moisture content of about 11% and aflatoxins of about 160 μg/kg, 10–20 kGy could be used to ensure product quality and effective decontamination. In practice, the irradiation dose can be appropriately reduced when the moisture is high and increased when the initial contamination content is high. In conclusion, the high-energy electron rays are a practical option for industry to effectively degrade aflatoxins in defatted groundnut cake due to their cost-effectiveness, having little impact on product's nutritional value, and quick and easy to use without new environmental pollution.