Based on the batch results, we constructed a simplified simultaneous saccharification and fermentation (SSF) model for the simulation of lactic acid production directly from unhydrolyzed potato starch using Lactobacillus amylophilus. The results of batch operation at different initial starch concentrations (20, 40 and 60 g/l) indicated that a higher initial starch concentration would lead to a slightly lower productivity, but would largely decrease the yield. Among that, the batch with 20 g/l of initial starch had the maximum productivity and the maximum yield, which would be 0.31 g/(l h) and 98% (g/g), respectively. In view of increasing the productivity and the final lactic acid concentration, a starch-controlled fed-batch operation with 20 g/l of initial starch was performed. It showed the fed-batch operation with starch controlled at 8 ± 1 g/l by adjusting the starch-feeding rate led to the maximum productivity of 0.75 g/(l h) and the yield of 69%.