Abstract: The efficient utilization of coarse feed resources—including forages, crop straws, and agricultural by-products—by ruminants is fundamentally dependent on the ruminal microbial degradation and fermentation of neutral detergent fiber (NDF), which is predominantly composed of cellulose and hemicellulose, as well as other fermentable structural carbohydrates such as pectin. Upon feed entry into the rumen, functional microbial populations initially adhere to the plant cell wall and secrete carbohydrate-active enzymes, subsequently releasing fermentable sugars that enter glycolysis to yield pyruvate, which is then further converted into volatile fatty acids (VFAs) such as acetate, propionate, and butyrate. Acetate, propionate, and butyrate are intimately associated with mammary lipogenesis, hepatic gluconeogenesis, and ruminal epithelial development, respectively, representing the major route through which energy from coarse feeds is transformed into host-metabolizable energy. Concurrently, the partitioning of fermentation-derived hydrogen, methanogenic archaeal activity, ammonia-N assimilation efficiency, and microbial crude protein (MCP) synthesis collectively determine the net retention of energy and nitrogen. Multiple factors, including dietary NDF level, physically effective NDF (peNDF), starch degradation rate, rumen-degradable protein (RDP) supply, degree of energy-nitrogen synchronization, host genetic background, and rumen developmental stage, can all modulate the synergistic and competitive interactions among fiber-adherent bacteria, lactate-utilizing bacteria, propionate-producing bacteria, methanogenic archaea, and protozoa. Following the conceptual framework of "coarse feed fiber characteristics - colonization by fibrolytic microorganisms - VFAs and MCP generation - host energy utilization, " this review synthesizes the current understanding of the mechanistic basis underlying rumen microbe-mediated fiber degradation and dietary energy utilization. Furthermore, we discuss the application prospects of dietary formulation strategies and exogenous intervention approaches in enhancing NDF digestibility, optimizing VFAs profiles, mitigating enteric methane losses, and improving nitrogen utilization efficiency, with the aim of furnishing a theoretical foundation for precision nutritional management of ruminants, efficient valorization of coarse feed resources, and low-emission ruminant production systems.