Abstract: The effect of single strain fermentation,mixed koji cultures,multi-strain mixed koji fermentation on the quality of soybean paste was studied by measuring the protease activity and amino nitrogen contents after 7 days of fermentation,Huniang 3.042 Aspergillus oryzae,AS 3.35 Aspergillus niger,AS 3.324 Aspergillus batatae,Huniang 3.130 Mucor,AS 3.972 Monascus,Rhizopus oryzae and Bacillus subtilis were used. The results showed that mixed koji cultures produced the highest levels of protease activity and amino nitrogen contents,followed by single strain fermentation and multi-strain mixed koji fermentation. 2 strains and 3 strains samples produced higher protease activity and amino nitrogen contents among the mixed koji cultures and multi-strain mixed koji fermentation. In the mixed koji cultures,the protease activity and amino nitrogen contents of the sample No. 5 containd Huniang 3.042 Aspergillus oryzae,AS 3.35 Aspergillus niger and Bacillus subtilis reached 713 U/mL and 0.89 g/100 g. The mixed koji cultures of Huniang 3.042 Aspergillus oryzae,AS 3.35 Aspergillus niger and Bacillus subtilis was more conducive to improve the quality of soybean paste.