Ultraviolet (UV) assisted zero-valent iron (ZVI)-activated sodium persulfate (PDS) oxidation(UV-ZVI-PDS) was used to treat waste activated sludge (WAS) in this study.The dewaterabil-ity performance and mechanism of WAS dewatering were analyzed.The results showed that UV-ZVI-PDS can obtain better sludge dewatering performance in a wide pH range (2.0-8.0).When the molar ratio of ZVI/PDS was 0.6,UV was 2S4nm,PDS dosage was 200 mg/g TS (total solid),pH was 6.54,reaction time was 20 min,the CST (capillary suction time) and SRF (specific resistance to filtration) were decreased by 64.0％ and 78.2％,respectively.The molar ratio of ZVI/PDS used in this paper is much lower than that of literatures,and the contents of total Fe and Fe2+ in sludge supematant remained at a low level,as 3.7 mg/L and 0.0 mg/L.The analysis of extracellular polymeric substances (EPS),scanning electron microscope (SEM) and particle size distribution showed that the EPS could be effectively de-stroyed by UV-ZVI-PDS,the sludge flocs broken down into smaller particles,cracks and holes appeared,and then the bound water was released.At the same time,the highly hydrophilic tightly bound-EPS (TB-EPS) were converted into loosely bound EPS (LB-EPS) and soluble EPS(S-EPS).During sludge pretreated by UV-ZVI-PDS,positively charged ions,such as Fe2+,Fe3+and H+,produced in the reaction system could reduce the electronegativity of sludge sur-face,promote sludge particles aggregation,and then enhanced the sludge dewaterability.