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Our study examined the relationships between riparian plant communities and their soil properties along the midstream of the Heihe River in northwestern China’s arid region. Significant variations in species composition were observed across the upper, middle, and lower reaches of this midstream (adonis2 and anosim, <i>p</i> < 0.001). The lower reaches exhibited higher species diversity (Shannon index up to 2.12) compared to the other reaches. Gramineous plants, particularly <i>Agropyron cristatum</i> (L.) Gaertn. and <i>Equisetum ramosissimum</i> Desf., dominated all reaches, with relative abundances exceeding 50% in the upper reach sites. The soil ionic concentration showed distinct spatial heterogeneity, peaking at site 9 (upper reaches) and lowest at site 3 (lower reaches). Species diversity indices negatively correlated with SO₄²⁻, Mg²⁺, and Ca²⁺ concentrations, while salt-tolerant species like <i>Agropyron cristatum</i> (L.) Gaertn. and <i>Phragmites australis</i> Trin. positively correlated with Na⁺ and Cl⁻ levels. Soil nutrients had weaker but notable effects on the distribution of <i>Onopordum acanthium</i> L. and <i>Artemisia argyi</i> H. Lév. and Vaniot. These findings suggest that riparian plant community distribution along the Heihe River is influenced by complex interactions between hydrological processes, salt dynamics, and soil physicochemical properties, such as anion and cation concentrations and electrical conductivity (EC). Our research provides valuable insights for understanding and managing riparian ecosystems in arid regions.