This study aimed to identify the best growth conditions for Bacillus subtilis N30 to produce viable cell counts, pH values, and protease activity through fermentation. The research employed response surface criteria and desirability function analysis. Box-Behnken and central composite designs (BBD and CCD) were used to determine the number of processing variables and experimental runs. The results of screening single factor experimental design as maltose content (0.5–1.5% w/v), malt extract concentration (0.25%–0.75% w/v), and incubation time between 30 and 42 h were applied for coded levels (−1, 0, +1) of each independent variable correlated to steps of 0.5, 0.25, and 6, respectively. Viable cell count, pH level, and protease activity were response variables. Analysis of variance (ANOVA) revealed no significant difference when using CCD but significant linear, quadratic, and interaction influences of fermentation parameters on the response of protease activity when using BBD. Both the BBD and CCD models did not fit the viable cell count and pH. According to numerical optimization, the ideal fermentation parameters were a maltose concentration of 1.19%, a malt extract of 0.56%, and a culture time of 33 h, with a predicted protease activity yield of 5.88 U/ml. This optimum condition for growing Bacillus subtilis N30 with high protease activity will be applied in the fermentation of soy milk since it contains many short-chain peptides (2–20 amino acids), which may help prevent and manage high blood pressure for human beings.