The rumen is a unique digestive organ of ruminants, with a rich microbial community structure inside. It can decompose indigestible feed into volatile fatty acids and other nutrients through degradation and fermentation, promoting the digestion and absorption and of the body. In recent years, based on metagenomic technology, extensive research has been conducted on the rumen microbiota of ruminants, and a relatively complete structure of the rumen microbiota has been obtained. This has elucidated its main functions within the host, which is crucial for studying the connection between rumen microorganisms and host phenotypes. It is also possible to improve growth performance by regulating the composition of rumen microbiota. The article reviews the research progress of rumen microorganisms in the absorption and digestion of carbohydrates, lipids, proteins, and other substances in ruminant animals, as well as energy loss, based on metagenomic technology. It aims to provide a reference for further research on the role of rumen microorganisms in regulating the absorption and digestion of ruminants.