In view of the problem that most blocks in Huabei Oilfield can not directly achieve the polymerization of produced water, the main components causing polymer viscosity decline in sewage were analyzed to determine the key influencing factors and clarify the mechanism. On this basis, the methods of reducing the viscosity loss of wastewater mixing were studied, and systematic laboratory tests were carried out for different water quality in Huabei oilfield, including XRD, infrared spectroscopy, scanning electron microscopy and other characterization methods, to find out the experimental effect, screen the optimal scheme, and realize the produced water mixing. The results show that the removal of Ca2+ and Mg2+ and the reduction of their mineralization are very important for the realization of wastewater polymerization and the improvement of recovery efficiency of high calcium and magnesium high mineralization reservoirs.