Abstract: In order to explore the community characteristics of culturable filamentous fungi in Nam Co Lake in spring, the composition and abundance of filamentous fungi were determined based on the isolation and purification, combined with morphological characterization and ITS sequence analysis. At the same time, water environmental factors were determined to analyze correlations between ecological differentiation of dominant species of filamentous fungi and environmental factors in Nam Co Lake. The results showed that a total of 921 filamentous fungi strains were isolated from Nam Co Lake. These strains were identified as 62 species in 20 genera. Fungus resources are abundant, among which, the dominant species (Y>0.02) include: Penicillium commune, Penicillium vinaceum, Penicillium polonicum, Penicillium goetzii, Penicillium griseoroseum, Mucor hiemalis, Mucor racemosus, Pleosporales sp.2 and Penicillium crustosum. The niche indices of the dominant species showed that the sum of ecological response rates of dominant species is negative, and low overlap species accounted for a large proportion (56.94%). Overall, there was a positive correlation among the dominant species, but it did not reach a significant level (χ²>3.841), indicating that the community was in a stage of decline. With weak competition and loose relationships and great differences in resource utilization or ecological adaptability among dominant species. Moreover, the dominant species have not reached a relative dynamic balance, and their succession has not reached the top stage. The correlation between environmental factors and dominant species showed that salinity, conductivity, chemical oxygen demand, turbidity and ammonium nitrogen are the main factors affecting the distribution of dominant species of filamentous fungi in Nam Co Lake. These studies provided basic data for correctly understanding the population characteristics of culturable filamentous fungi in plateau lakes and laid a foundation for the development and utilization of culturable filamentous fungi.