Abstract: S^2-, Fe²⁺ and bacteria in oilfield produced water could degrade polyacrylamide and decrease the polymer solution's viscosity seriously. An Mn Ce complex oxide catalyst was prepared by impregnation method to treat oilfield-produced water by multi-phase catalytic oxidation, The results showed that the catalyst was high effective and stable. The viscosity of the polymer solution made of simulated oilfield produced water processed by the oxidation was 5.48 times higher than that unprocessed.