Objective To purify and study the enzymatic properties of acid protease from the Trichoderma reesei strain, and to screen the stabilizer formula.Methods The acid protease is purified by ammonium sulfate precipitation, dialysis, and anion exchange column chromatography. Then, its molecular weight is determined by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and its enzymatic properties are studied. Finally, the stabilizer formula of acid protease is optimized, with an investigation into its effect on acid protease storage stability.Results For the purified acid protease, its specific enzyme activity is 4 849 U/mg, purification fold is 3.28 times, and relative molecular weight is 40. The optimal reaction condition of the enzyme is a pH of 3.0 and a temperature of 55 ℃, with satisfactory stability in the pH range of 3.0 to 6.0 and below 60 ℃. The enzyme activity retention rate is 69% at 60 ℃, indicating high temperature resistance. In metal ions, Na⁺, Zn²⁺, and Mn²⁺ protect acid protease stability. Stored at a concentration of 20% sodium chloride for 7 days, acid protease still retains certain activity, exhibiting high salt tolerance. The optimal formula of acid protease stabilizer is: maltose 26%, mannitol 12.5%, sodium chloride 12%, and zinc chloride 0.1 mol/L. Added with stabilizer, the enzyme activity of acid protease is 92.8% after storage at 45 ℃ for 48 days.Conclusion Acid protease is high in heat and salt resistance, while the stabilizer formula can significantly improve acid protease stability.