Abstract: Enhancing the hydrolysis efficiency of maize stover is often crucial for its efficient anaerobic fermentation (AF) to produce methane. However, conventional biological pretreatments are commonly confined to long cycle times and the high cost of the single physicochemical approaches. This study aims to investigate the effects of combined pretreatment with oxygen nanobubble water (O₂-NBW) and composite microbes on the degradation of the maize stover and its subsequent AF for methane production. Firstly, a systematic analysis was implemented to explore the effects of a combined pretreatment with the composite microbes and O₂-NBW on the degradation of maize stover at different inoculation ratios (ranging from 1:1 to 4:1). Both environmentally friendly and efficient pretreatment was selected to determine the optimal inoculation ratio. Four pretreatments were performed—namely, deionized water (DW), a single microbial consortium, O₂-NBW, and the combined composite microbes with O₂-NBW—on the methane production of maize stover during AF. An exergy analysis of the anaerobic fermentation was subsequently conducted after pretreatment. Results demonstrate that the optimal inoculation ratio of the composite microbes was consistently 4:1 under all tested conditions. The O₂-NBW pretreatment group showed significantly higher peak levels of the reducing sugars and chemical oxygen demand (COD), compared with the control. The synergistic pretreatment with the O₂-NBW and composite microbes also outperformed the DW pretreatment at the optimal ratio. The exergy efficiency of anaerobic fermentation was improved by 70.99%. Specifically, the peak daily methane production increased by 24.40% to (14.02 ± 0.3) mL/(g·d), while the cumulative methane yield also rose by 37.40% to (139.57 ± 4.5) mL/g. Kinetic analysis with the modified Gompertz model revealed that the combined pretreatment group shared the shortest lag phase (λ=1.63 d), which was 23.8% shorter than the control group (2.14 d), indicating the higher microbial acclimatization and metabolic initiation. The maximum methane potential (M₀) of 139.57 mL/g was obtained to represent the more efficient substrate conversion in the group. Notably, the maximum methane production rate reached 13.83 mL/(g·d), representing a 35.3% improvement over the control group, 10.22 mL/(g·d), indicating the significant enhancement of reaction kinetics after pretreatment. Process monitoring during the methanogenic phase showed that the combined pretreatment group exhibited the rapid hydrolysis-acidification (sharp pH value drop and reducing sugar surge) followed by highly efficient methane production (peak methane concentration of 66.33% ± 1.2%). The pH value decreased rapidly from the initial 7.2 to 6.65 ± 0.04, while the peak reducing sugar concentration reached (221.80 ± 3.36) mg/L, with a 31.5% increase, compared with the control group (168.00 ± 4.61) mg/L, indicating the effective depolymerization of lignocellulose after pretreatment. Exergy analysis highlights that the energy efficiency of the combined pretreatment, with an exergy efficiency of 15.80%, thus surpassing the composite microbes alone (14.92%), O₂-NBW alone (10.07%), and the DW control (9.24%). The O₂-NBW's micro-oxygen environment was attributed to enhancing the activity of composite microbes-derived ligninolytic enzymes for the lignocellulose deconstruction. Thereby, the energy losses were reduced to optimize the metabolic efficiency. In conclusion, the O₂-NBW and composite microbes were combined to significantly enhance the degradation of maize stover in the pretreatment, with a shorter microbial lag phase, and high efficiency for methane conversion. The irreversible system losses were reduced for the high methane yield during energy conversion. These findings can provide a feasible strategy to develop the low-energy, short-cycle, and high-efficiency pretreatment for the anaerobic fermentation of lignocellulosic biomass.