Altering recalcitrant structures of bamboo is essential to obtain high yield of bioethanol via bioconversion process. With the goal of improving cell wall digestibility, alkaline liquid hot water was used to pretreat N. affinis. The effects of temperature and alkali dosage on structural alterations were determined by chemical composition, Brunauer Emmett Teller (BET) and gel permeation chromatography (GPC). The relationship between these changes and substrate digestibility was addressed by separate enzymatic hydrolysis and fermentation (SHF). The results indicated that pretreatments partly removed and degraded hemicelluloses and lignin, reducing yields of substrates and molecular weights of carbohydrates. With the change of cell wall structure, specific surface area of materials increased after LHW pretreatment but decreased with further removal of lignin and hemicellulosic fractions. Maximum bioconversion was obtained by pretreatment with 0.5% NaOH aqueous at 170 degrees C and SHF, yielding 4.8 g/L ethanol.