Achieving the capacity to produce fermentable sugars from lignocelluloses via green and efficient approaches is of strategic significance to an environmentally sustainable society. In this work, a novel wet-mechanochemical pretreatment approach was proposed using small amount of dilute alkali-assisted ball milling and subsequently hydrothermal pretreatment at mild conditions to enhance the enzymatic saccharification efficiency of bagasse and pennisetum. Effects of pretreatment conditions, such as NaOH concentration, hydrothermal reaction temperature and time, on the reducing sugars production were systematically evaluated. Parameters were optimized by statistical analysis and response surface methodology. Results showed that the existence of small amount of dilute alkali during ball milling can greatly facilitate the subsequent saccharification of bagasse and pennisetum, which can reduce the alkali dosage in comparison with traditional biomass pretreatment approach. The highest reducing sugars yield of 40.75% could be obtained from bagasse after pretreated by final concentration of 0.4% alkali in hydrothermal pretreatment process at 100 degrees C for 40 min. 55.74% of reducing sugars could be obtained from pennisetum treated by final concentration of 0.4% alkali in hydrothermal pretreatment process at 80 degrees C for 60 min. Compared with pretreatment temperature and time, NaOH concentration had more impact on the reducing sugars yield. Chemical composition of lignocelluloses also showed great influences on their saccharification efficiency. This work provides feasible theoretical basis and method for the efficient utilization of lignocelluloses.