Abstract: Nano sized zero valent iron was prepared by liquid-phase reduction method and characterized by SEM and XPS, the changes of structure and valence state of elements before and after the reaction of nano zero valent iron with peroxymonosulfate were analyzed, the results showed that the surface of nano zero valent iron was oxidized; With atrazine as the target pollutant, peroxymo-nosulfate as oxidant, methanol and tert butyl alcohol as free radical quenchers, the reaction mechanism of atrazine degradation by nano zero valent iron activated persulfate was deduced by combining the change of peroxymonosulfate concentration during the reaction and the iron content in the solution after the reaction, · SO4-and · OH were the main oxidation active species for atrazine degradation. Compared with micron zero valent iron, the effect of zero valent iron size on atrazine degradation was investigated,the smaller the size of zero valent iron, the better the effect of PMS activation; Nano zero valent iron was recycled twice, and the possibility of reuse was discussed. After two times of recycling, nano zero valent iron still maintained good activation effect.