Abstract: As the largest city in Northwest China, the water ecological environment of Xi’an has been severely damaged with the expansion of city and the development of industrialization. In water ecological health assessment, phytoplankton can objectively evaluate water quality and nutritional health status of water bodies. In order to determin the relationship between structural characteristics of phytoplankton communities and environmental factors in the Xi’an city, the composition of phytoplankton community, phytoplankton cell density and phytoplankton biomass of 24 sampling points in the Bahe, Chanhe, Fenghe and Heihe River were investigated on October 2020 and June 2021. The results showed that 115 species of phytoplankton in 6 phyla were identified during the dry season. The main species include 11.30% Cyanophyta, 54.78% Bacillariophyta and 26.96% Chlorophyta. The average cell density of phytoplankton was (3.36±3.50)×10⁶ cells/L, and the mean biomass was (1.79±3.59) mg/L. In addition, 168 species of phytoplankton were identified in 7 phyla during the wet season. The main species include 7.74% Cyanophyta, 51.79% Bacillariophyta and 29.76% Chlorophyta. The average cell density of phytoplankton was (9.17±9.73)%×10⁶ cells/L, and the mean biomass was (6.54±11.57) mg/L. Compared with the dry season, the number of species, cell density and biomass in the wet season were larger than those in the dry season. Furthermore, the results of cluster analysis showed that the phytoplankton community structure and water environment condition were similar among most sampling points in the Xi’an urban river, and human interference may be the main reason for the spatial differences in the remaining points. The results of redundancy analysis (RNA) showed that the main environmental factors determing the distribution of phytoplankton community structure in urban river in the Xi’an city were temperature (Temp), ammonia nitrogen (NH₃-N), pH, dissolved oxygen (DO), river width (Wide) and chlorophyll (CHL). Therefore, comprehensively considering the environmental factors, biodiversity index, phytoplankton community structure and dominant species showed that the water quality of Heihe River is the best among the four river systems, the water quality of Bahe River and Fenghe River is in average level, and the water quality of Chanhe River is poor.