The chemical substances in urban rivers influence municipal water systems and reflect the recent use of these chemicals by humans or industries around the urban center. In this study, seven perfluoroalkyl substances (PFASs)—perfluorohexanoic acid (PFHxA), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), 2-perfluorohexyl ethanol (6:2 FTOH), 2-perfluorooctyl ethanol (8:2 FTOH), and 6:2 chlorinated polyfluoroalkyl ether sulfonic acids (F-53B)—could be detected and quantified in river water and sediment samples collected from one tributary of the Liuxi River, which is part of Pearl River near Guangzhou in Guangdong province, South China. The fluxes of target PFASs into Liuxi River and their related ecological risks were further estimated. The total concentrations of PFASs (ΣPFASs) ranged from 506 to 3.16 × 10³ ng/L in water samples and 9.13 to 850 ng/L in sediment samples. The two dominant PFAS compounds were 6:2 FTOH and PFHpA, which accounted for more than 90.0% of ΣPFASs in river water and sediment. Correlation analysis showed that there was significant positive correlation (p < 0.01) between two selected PFASs (e.g., between 6:2 FTOH and PFHpA). Correlation analysis of PFASs in river water and sediment indicated most PFASs in sediment were partitioned from river water. The ecological risk assessment indicated that the detected PFASs have a low risk (HQ < 0.1) in river water and sediment to Daphnia magna in the Liuxi River.