Abstract: Per- and polyfluoroalkyl substances (PFASs), as a class of persistent, bioaccumulative, and toxic synthetic pollutants, have drawn global attention due to their environmental behaviors and health risks. However, the absence of PFASs standards in domestic water quality regulations hinders ecological risk assessment. Focusing on the Jiyun River, a major inflow river into Bohai Bay, this study quantified 22 PFASs in surface water using liquid chromatography-mass spectrometry, analyzed their spatiotemporal variations between wet and dry seasons, derived water quality criteria (WQC) through the Species Sensitivity Distribution (SSD) and assessment factor methods, and evaluated ecological risks in the watershed using the entropy method. Key findings were as follows: 1) PFASs concentrations in the Jiyun River exhibited higher levels during the wet season (5.70-75.23 ng/L) than the dry season (4.08-46.57 ng/L), with spatial distribution showing downstream > upstream. 2) SSD-derived WQC for PFOA and PFOS were 407.51 and 87.47 ng/L, respectively, both lower than the US recommended values. Assessment factor method yielded WQC ranging 100-24 600 ng/L for 8 PFASs, including PFBA and PFHxA. 3) Entropy-based risk assessment revealed that all hazard quotient (HQ) values were below 0.1 across the basin, except for PFOA at midstream sites J7-J8 (HQ=0.100) during the wet season and PFHxA at downstream sites J10-J12 (HQ=0.165 to 0.214, low risk). The study demonstrates spatiotemporal heterogeneity of PFASs pollution in the Jiyun River, with higher concentrations during the wet season and more significant pollution downstream. While current ecological risks remain generally low, low risks exist in some locations, and persistent accumulation of PFOA and PFOS may pose long-term threats to benthic organisms.