Abstract: In order to understand the community structure characteristics of culturable cellulose-decomposing fungi in soils from different ecosystem in the Sanjiangyuan Regions, the fungi in soil from four typical grassland types were isolated by dilution plate method using a sodium carboxymethyl cellulose plate medium. The population dominance index, Shannon-Wiener index, evenness, niche breadth and community similarity were employed to analyze the community structure of the isolated fungi. The results showed that the amount and species distribution of culturable cellulose-decomposing fungi varied strongly by ecosystem. Species number decreased in the following order: shrub grassland>alpine meadow>Kobresia tibetica grassland>grass pasture. In total 17 genera were isolated from the four grassland types. The population dominance index, species diversity index and evenness index of fungi from grass pasture were highest, whereas the population dominance and species diversity indices from alpine meadow were lowest. Analysis of community similarity between the different ecosystems showed that fungi in shrub grassland and Kobresia meadow soils had the highest similarity. The similarity coefficient for fungi in grass pasture and Kobresia tibetica grassland soils was the lowest. The results of niche breadth analysis indicated that the species of Mucor, Fusarium, Mortierella and Penicillium had wider niche breadth and adaptability, while the species of Didymella, Thielavia and Humicola had narrower niche breadth and adaptability. The study thus shows that the diversity and community structure of soil cellulose-decomposing fungi are closely related to ecosystem types.