To optimize the fermentation conditions with index of amino acid nitrogen content for inspection of soy sauce fermented by aspergillus oryzae As3.042 by the response surface method. Firstly, the experiment was to determine the optimum fermentation conditions at 40 d of temperature, density of adding salty water and addition of salty water by using single factor experiment. On the basis of single factor experiment with amino acids as examining index, fermentation temperature, density of adding salty water and addition of salty water was optimized by using response surface analysis. the result was gotten, the optimum process for the temperature of 40.28 ℃, density of adding salty water of 9.66%(the percentage of quality) and addition of salty water of 74.70%(the percentage of volume). Under the condition of fermentation, the content of amino acid nitrogen is 0.837 6 g/kg, close to the theoretical value (0.841 g/kg), can provide the basis for practical production.