Abstract: In order to investigate the relationship between phytoplankton species in different dimensions of time and space and their utilization of environmental resources in Jiangsu Section of the lower reaches of the Huaihe River, 5 rivers were selected as research objects and 18 sampling sites were set up for investigation during the wet season from 2019 to 2022. A total of 238 phytoplankton species belonging to 89 genera and 8 phyla were identified. The dominance index, niche width, niche overlap value and ecological response rate were calculated, and the niche characteristics of dominant species of phytoplankton were analyzed in three dimensions of time, space and space. The results showed that 12 dominant phytoplankton species are identified during the study period, among which Oscillatoria irriguum, Phormidium planctonica and Microcystis aeruginosa are the common dominant species during the four years, all belonging to the phylum cyanophyta. The niche widths of dominant species showed that the temporal niche widths exhibited the greatest variability, ranging from 0.406 to 0.945, followed by the spatial niche widths, from 0.175 to 0.647, and the spatio-temporal widths proved the narrowest, from 0.054 to 0.396. The specie exhibiting the smallest niche width across all dimensions was Merismopedia punctata, whereas Ulothrix subtillissima demonstrated the widest niche width in the temporal and spatial, which showed strong ecological adaptability. Examination of niche overlap values unveiled that proportions exceeding 0.6 were 57.58%, 27.27% and 15.15% within the temporal, spatial and spatio-temporal dimensions, respectively. This distribution indicated a dominance of high, moderate and low niche overlaps across the respective dimensions. Furthermore, the sum of ecological response rate displayed positive in both the temporal and spatial dimensions, but negativity within the spatio-temporal dimension. This observation implies that community structure maintains higher stability within the spatio-temporal dimension compared to the temporal and spatial dimensions. In summary, the phytoplankton in Jiangsu Section of the Huaihe River Basin exhibited limited temporal variation, relatively overlapping dominant species, great spatial variation and large differences in dominant species. The evident high degree of niche differentiation across the phytoplankton community suggests weak interspecific competition and a relatively stable community structure.