The main factors that affected the viscosity reduction of the polymer solution prepared with Chengdong sewage from Shengli Oilfield were studied through the orthogonal analysis. Taking into consideration of the main factors from Chengdong sewage, the viscosity increasing agent was developed, the viscosity of polymer solution prepared with treated sewage could be increased from 12 mPa·s to 32 mPa·s, increasing by 167%; The increasing -viscosity mechanism could be analyzed by AFM and DLS , on the one hand, the method of precipitation with NaOH could eliminate the impact on polymer aggregates from Fe²⁺, and the particle size of polymer aggregates increased from 80.5 nm to 159.9 nm; on the other hand, Ca²⁺, Mg²⁺ could be shielded by the ion shield agent ,so that the crimp effect of polymer molecular chain from Ca²⁺, Mg²⁺ was reduced; and polymer aggregates size increased from 160.1 nm to 208.5 nm.