Abstract: Sweet sorghum, characterized by its elevated saccharide content and substantial lignocellulosic biomass, has emerged as a highly promising candidate for bioenergy production through biomass conversion technologies. However, the intricate lignocellulosic network structure within sweet sorghum poses a significant barrier to the accessibility of anaerobic microorganisms and enzymes, resulting in reduced hydrolysis efficiency and digestion reaction kinetics. Considering the seasonal harvesting pattern of sweet sorghum, the development of effective storage and pretreatment methodologies capable of simultaneously disrupting the lignocellulosic anti-degradation barrier is crucial for enhancing its bioenergy conversion efficiency. This study conducted a systematic comparative analysis to investigate the effects of various additives on the bio-augmented pretreatment of ensiled sweet sorghum and their subsequent impact on methane production during anaerobic digestion. The research evaluated the influence of four distinct additives, such as rumen fluid, biogas slurry, cellulase, and xylanase on the lignocellulosic composition alterations and microstructural changes of sweet sorghum. The investigation aimed to discern the variances impacts of via bio-augmented pretreatment on the bioenergy conversion benefits of sweet sorghum, in terms of the methane production process, digestive fluid characteristics, and system stability. The results revealed that, in comparison to the un-ensiled sweet sorghum, the bio-augmented ensiling pretreatment significantly reduced the content of hemicellulose and lignin in sweet sorghum by 14.67%-30.99% and 10.30%-47.23%, respectively, while the cellulose content increased by 6.32%-35.93%. Additionally, the relative crystallinity index (CrI) of ensiled sweet sorghum increased by 1.34%-13.08%. Furthermore, the extension of pretreatment time was found to progressively facilitate the disintegration of lignocellulosic anti-degradation barrier structure. It was found that the complex microbial communities and enzyme systems in biogas slurry and rumen fluid have a superior disruptive effect on the anti-degradation structure of ensiled sweet sorghum. The anaerobic digestion process maintained exceptional operational stability, with optimal pH (7.73-8.25) and ammonia nitrogen concentration (1350-1600 mg/L) ranges throughout the anaerobic digestion period. The ensiling pretreatment could effectively increase the removal rate of chemical oxygen demand (COD) by approximately 11.81%-34.32% and shortened the anaerobic digestion lay phase (0.8-1.37 days). All ensiling pretreatment strategies resulted in an average increase of 24.32% in daily methane production, while the CK showed the highest cumulative methane enhancement (49.16%), which attributable to the optimization of the volatile fatty acids (VFAs) composition. From an economic perspective, methane production benefits were significantly higher in all ensiled pretreatment groups compared to the un-ensiled sweet sorghum. Particularly, biogas slurry emerged as the most economically viable bio-augmentation additive, demonstrating a substantial economic benefit of 681.73 yuan/t. This study provides critical insights into the efficacy of bio-augmented ensiling pretreatment for enhancing the energy conversion efficiency of sweet sorghum, with particular emphasis on the strategic use of biogas slurry as an additive. The substantial economic and environmental advantages of this approach significantly contribute to advancing sustainable biomass conversion strategies, which are imperative for the shift towards a renewable and eco-friendly energy sector. Consequently, considering the practical situation of large-scale biogas projects, it is recommended to utilize biogas slurry as an additive for the enhancing pretreatment of sweet sorghum. This approach not only enhances the energy conversion efficiency of sweet sorghum but also mitigates the costs associated with of biogas slurry, thereby facilitating the recycling of biogas slurry resources for the large-scale biogas plant.