Abstract: Per- and polyfluoroalkyl substances (PFAS) are new pollutants under key control in China, and wastewater treatment plants are important nodes for their entry into water bodies. Most of the current wastewater treatment plant processes are integrated after upgrading, and the removal effects of PFAS by each process are different. In order to explore the removal effect of the current typical upgraded wastewater treatment processes on PFAS, the characteristics and concentration of PFAS components in each operating unit of the improved A²O and improved OD processes in a sewage treatment plant in Beijing were analyzed, the contribution of different units to the removal of PFAS components was studied, and the effect and mechanism of the removal of PFAS by the two processes were discussed. The results showed that: (1) The short-chain substitution effect had emerged within the scope of the treatment plant, and the main PFAS in the influent of the two typical wastewater treatment processes were perfluoropentanoic acid (PFPeA), perfluorobutanoic acid (PFBA) and perfluorobutane sulfonate (PFBS). (2) The decomposition of PFAS precursors caused by biochemical treatment units and ultraviolet disinfection tanks, and the interception, filtration, adsorption and precipitation of PFAS by grates, MBR tanks and sedimentation tanks were important mechanisms for the change of PFAS occurrence characteristics in the two typical wastewater treatment processes. (3) The overall removal efficiency of total PFAS concentration by improved A²O and OD processes was 60.65% and 82.62%, respectively. The former had a prominent removal effect on PFPeA and PFBS, while the latter had a good removal effect on all short-chain PFAS except perfluorohexanoic acid (PFHxA). The upgrading of the wastewater treatment processes has improved the removal effect of some PFAS to a certain extent, and especially the improved OD process has a better removal effect on PFAS.