Abstract: Aflatoxin B₁ (AFB₁) is one of the most carcinogenic chemicals, posing a serious threat to the food and feed industries. In this study, the fermentation and degradation conditions by Pseudomonas aeruginosa M4 were optimized to improve the degradation efficiency on AFB₁. Single factor test was applied based on the evaluation index of strain growth and AFB₁ degradation rate. The results showed that the conditions of inoculum volume of 5%, liquid volume of 25 mL/250 mL, initial pH value of 7.0, fermentation temperature of 37℃ and fermentation time of 48 h are conducive to the degradation of AFB₁, and the degradation rate of AFB₁ increased to 47.65%. The response surface optimization experiment was carried out by Box-Behnken design. The initial pH value, fermentation temperature and fermentation time were used as the response variables, and the AFB₁ degradation rate was set as the response value. The optimal fermentation conditions are as follows:the initial pH value was 6.80, the fermentation temperature was 36.0℃, and fermentation time was 56.0 h. The highest degradation rate of AFB₁ was 52.84%, which was not significantly different from the predicted value (P> 0.05). The effect of degradation conditions on the degradation of AFB₁ by fermentation supernatant was studied, and the results showed that the degradation temperature significantly affected the degradation rate of AFB₁. In the temperature range of 30-60℃, the degradation rate of AFB₁ increased with the increase of the fermentation temperature. At the same degradation temperature, with the extension of degradation time, the degradation rate of AFB₁ gradually increased and then tended to be stable. After 6 hours of degradation at 95℃, the degradation rate reached 96.17%, which was much higher than the degradation rate before optimization. In addition, 0.01 mol/L Fe³⁺, Mg²⁺ and Zn²⁺ metal ions can significantly inhibit the degradation process of AFB₁, and Fe³⁺ had the most significant inhibitory effect, reducing the degradation rate of AFB₁ from 93.85% to 20.85%. However, Cu²⁺ and Mn²⁺ ions promoted the degradation of AFB₁. In this study, the optimized fermentation condition significantly increased the degradation rate of AFB₁ from 34.10% to 96.17%, and this study provided a theoretical basis for the application of the degrading bacteria in the food and feed industries.