Effects of severe and mild alkaline hydrogen peroxide (AHP) pretreatment on ethanol production from sweet sorghum bagasse via pre-simultaneous saccharification fermentation, and the chemical structure changes of the substrates were investigated. The results showed that the bagasse pretreated by severe AHP could produce more ethanol than that of mild AHP. The maximum ethanol concentration of the bagasses from mild and severe AHP pretreatment with 8% bagasse loading was 7.642±0.140 g/L and 19.330±0.085 g/L, respectively. Moreover, the FTIR and NMR analysis illustrated that the molecule and surface structures of the pretreated bagasse were significantly changed compared with the control. The potential biomass energy production of the effluent from the pretreatment was also briefly discussed for future utilization of waste solution.The heat energy potentials of waste solution with severe and mild AHP pretreatment were 367.2 kJ/L effluent and 327.6 kJ/L effluent, respectively.