Abstract: Large amount of processing waste produced by the food industry is increasing every year, as the rising demands for crop production by growing human population. Currently, most of the waste is usually discarded, only part of which can be utilized to produce value-added products to some extent. The dispose of food processing waste has posed serious management problems on environmental protection. Alternatively, many of these residues with the nutritional value have the great potential to be reused into other production systems, in order to reduce a great loss of valuable materials, from the economic and environmental point of view. Specifically, most food wastes are rich in protein, starch, cellulose, and monosaccharides, mainly fructose and glucose. However, the high moisture content has been identified as a major obstacle to the management of biodegradable food processing waste. It is necessary to develop an upstream storage, and thereby to meet the requirement for a constant supply of utilization for bioenergy and ruminant feed. Ensiling can be an efficient way to preserve biomass with very low fermentation loss, particularly for the cyclic utilization of food processing waste. Using the silage theory, the present study aims to perform the co-ensiling of grain stillage and inulin processing residue from Helianthus tuberosus, and thereby to prepare the fermented forage with well-quality. Two by-products were co-fermented with eight mixing ratios of 1:0, 4:1, 2:1, 1.2:1, 1:1.5, 1:2.7, 1:7 and 0:1. The dynamic changes of nutritional components, lignocellulosic components and fermentation characteristics were investigated at 10, 30 and 60 days, respectively. A high throughput sequencing technique was used to analyze the microbial community diversity during ensiling. The results showed that the contents of neutral detergent fiber, acid detergent fiber and acid detergent lignin in silages at the ratio of grain stillage and inulin processing residue for 1.2:1 (M5) and 1:1.5 (M6) were significantly lower than that of other silages (P<0.05), accompanied by the higher content of soluble carbohydrates, resulting in the relative superior feed value and biodegradation potential at 60 days. The fermentation characteristics, including pH, the content of ammonium nitrogen and lactic acid in all silages, were in the range of excellent fermentation quality, indicating the excellent V-score scores (≥88). During the sole fermentation of grain stillage or inulin processing residue, the dominant bacteria at phylum level were Proteobacteria and Firmicutes. There was a remarkable change of bacterial community after co-ensiling fermentation. Firmicutes phylum and acid-tolerance lactic acid bacteria Lactobacillus dominated in the co-silages of grain stillage and inulin processing residue, respectively. Ensiling fermentation can be considered as a competition process between lactic acid bacteria and undesirable microorganisms, whose result can largely determine the silage quality at the different mixing ratios. The fermentation quality at the ratio of 1.2:1 and 1:1.5 for silages at 60 days were excellent, indicating that the grain stillage and inulin processing residue can achieve the high-quality ensiling by the synergistic effect in terms of biochemical characteristics. Considering the utilization and efficiency of biomass, it is suggested that the co-ensiling fermentation of grain stillage and inulin processing residue was performed at the mixed ratio of 1.2:1 for 30 days in the actual production. It infers that the co-ensiling fermentation is an effective approach for food processing waste. The finding can offer new promising possibilities for the solution of environmental pollution that induced by processing waste in food industry.