The response surface is effective to optimize SSF of sweet sorghum bagasse. ► Maximum ethanol yield, concentration and rate were obtained at different conditions. ► 25 FPU cellulase/g-glucan, 1.4 g yeast/L and 10% bagasse at 37 °C were recommended. ► Ethanol at 89.4% yield, 38 g/L concentration and 1.28 g/L/h production rate obtained.