Abstract: The preparation of compound protease solution which fermented by mixed mucedine consist of Aspergillus niger, Aspergillus oryzae and hair mould was researched.On the basis of single factor experiment, technological parameters of preparing compound protease were determined by mixture design method to optimize fermentation conditions as following:inoculum size of mixed mucedine was 2%, the ratio of Aspergillus niger, Aspergillus oryzae and hair mould was 1.59 ∶1 ∶1.95, pH was 5, incubation temperature was 30℃, incubation time was 72 hours.Under the condition of the fermentation process, compound protease solution with high enzyme activity was prepared.Debitterizing experiment was carried out with enzymolysis of soybean peptide by compound protease solution.The experimental results showed that best debitterizing conditions as followings:concentration of protease was 70U/mL, enzymolysis pH was 5, enzymolysis temperature was 60℃, enzymolysis time was 2 hours.Under the condition, the yield of short peptide was higher, the bitter taste value was lower, and effect of debitterizing was better.