Abstract: In order to investigate the phytoplankton functional groups distribution and its driving key factors, sixteen sampling sites were selected of the Yellow River Basin in Henan Province, involving two main streams, eleven tributaries and three reservoirs, from June to July, 2021. According to the analysis of phytoplankton composition, distribution of phytoplankton functional groups and the relationship between phytoplankton and environmental variables, results showed that (1) a total of 154 species belonging to 65 genera and 7 phyla were identified, mainly including Bacillariophyta, Cyanophyta, Chlorophyta, Dinoflagellata, Euglenophyta, etc. In terms of species abundance, Chlorophyta (68 species)>diatom (60 species)>Cyanophyta (11 species); Cyclotella sp., Auracoseira Granata var. angutissima, Aphanizomenon sp. and Pseudoanabaena sp. are the main dominant species in the basin (dominance≥0.02), among which diatom is absolutely dominant and Chlorophyta is sub-absolutely dominant. (2) Phytoplankton in the Yellow River Basin in Henan Province are classified into 23 functional groups, namely assemblage B, C, D, E, F, G, H1, J, L_M, Lo, M, MP, N, P, S1, T, W1, W2, X1, X2, X3, X_ph and Y; the spatial distribution of functional groups in the investigated basin is quite different. The functional groups in main stream are the least and tributaries are the most, the functional groups C, D, MP, P and J that adapt to eutrophic and mixed water bodies are dominant. (3) RDA analysis showed that the dominant functional group C was negatively correlated with TN. MP was negatively correlated with TP, \rmNH^+_4 -N, WT, pH and COD_Mn. Functional group P was positively correlated with \rmNH^+_4 -N, WT and COD_Mn. Functional group D was positively correlated with TN, functional group J was positively correlated with NTU, and strongly negatively correlated with DO. Among them, COD_Mn was the key factor driving the distribution of algal functional groups. (4) Combined with surface water environment assessment, Q and Shannon-Wiener index, the Yellow river within Henan Province is suffering heavy-nitrogen pollution, whereas the reservoir is also slightly polluted by phosphorus. In addition, it was suggested the Luohe River basin is more polluted than other tributaries.