The rumen of ruminants is known as a natural fermenter with the strongest fiber-degrading ability. The various microorganisms inhabiting the rumen confer it the ability to digest plant feed. As a group of microorganisms with low abundance in the rumen, anaerobic fungi are the first to colonize the cellulosic feed ingested by host animals and degrade lignocellulose by secreting massive efficient carbohydrate-active enzymes. However, due to the lack of sufficient genomic information and an effective genetic operating system for anaerobic fungi, the research on fiber-degrading enzymes secreted by anaerobic fungi and their degradation mechanisms is limited. This paper summarized the taxonomy and published genome information of the anaerobic fungi in the rumen, introduced the fiber-degrading enzymes and the structure and catalytic mechanism of cellulosomes, and recapitulated the applications of such enzymes in biomass energy, feed processing, textile, papermaking, and food processing. Studying the properties of fiber-degrading enzymes in anaerobic fungi will improve our understanding of their ability to degrade lignocellulose and their competition for resources in a highly complex rumen environment. Further, it will help us to learn the application potential of the enzymes in biotechnology and provide new strategies for the application of the enzymes in industries.