Abstract: The understanding of food web structure is fundamental to revealing trophic interactions, identifying key species, and elucidating the mechanisms that maintain ecosystem stability. Large mammals perform critical ecological functions in boreal forests, yet direct observation of their feeding relationships remains challenging. As a result, the scientific community still lacks a comprehensive understanding of the overall architecture of mammalian food webs and the relative roles of different trophic groups. This study focused on the Heilongjiang Huzhong National Nature Reserve, a representative boreal forest ecosystem in the Greater Khingan Mountains of Northeast China, to investigate the food web structure of dominant mammals. The objectives were to clarify the key species and major trophic interactions within the typical boreal forest ecosystem and to provide a scientific basis for ecosystem conservation and ecological health assessment. The study employed fecal DNA metabarcoding to determine trophic interactions among mammals and their food resources, reconstructed the food web through ecological network analysis, assessed species importance using degree centrality and abundance-weighted degree metrics, and identified key species and major trophic links critical to ecosystem functioning from the constructed network. A total of eight host species were identified, including three carnivores (Lynx lynx, Canis lupus, and Martes zibellina), two omnivores (Ursus arctos and Sciurus vulgaris), and three herbivores (Alces alces, Moschus moschiferus, and Capreolus pygargus). The three ungulates exhibited the highest connectivity in the food web. Among them, moose linked diverse plant resources and multiple carnivores, occupied a central position, and played a key role in maintaining trophic connectivity. Among carnivores, lynx showed the highest centrality, reflecting its broad prey spectrum and its strong regulatory influence on food web structure. Although sample sizes for brown bear and Eurasian red squirrel were relatively limited, both also displayed high connectivity, suggesting that omnivores can link multiple trophic levels and significantly enhance network connectivity. Among plant resources, species in Ericaceae and Coniferopsida had the highest abundance-weighted mean degree (wMD), highlighting that these plants serve as the primary food source for forest mammals and play a dominant role in sustaining trophic interactions. The results demonstrate that large ungulates underpin species interactions across trophic levels and form the structural backbone of the boreal forest food web. Omnivores enhance network complexity through their diverse feeding habits, and large carnivores strengthen trophic connectivity and facilitate species coexistence through broader diets. These different trophic groups exhibit functional complementarity, collectively maintaining the structural organization and system stability of the boreal forest food web. This study provides one of the first DNA metabarcoding-based reconstructions of a mammalian food web in the Greater Khingan Mountains and offers a scientific basis for biodiversity conservation, ecosystem management, and the identification of priority species for conservation in boreal forests.