Through analyzing the polymer viscosity of the oilfield sewage,the effect of S2-ion on polymer viscosity and the change rule of polymer viscosity were researched.According to the IR,NMR data before and after S2-ions decreasing the polymer viscosity,the mechanism of S2-ions lowering the polymer viscosity was studied.The results show that the polymer viscosity decreases with S2-concentration increasing.6 mg/L S2-ion can make 1.7 g/L polymer solutions viscosity drop to less than 10 mPa·s.The polymer solution collocated by simulated wastewater containing S2-products C=C double bond apex in the wave number 3 100 cm-1 and the chemical displacement of 6.00.The solution produces new double bond matter.The radical chain reaction occurs in the process of viscosity reduction,which makes polymer long chain break into small molecule.The polymer viscosity can be retained by inhibiting the production of radicals.