Abstract: In view of the plugging problem caused by long-term polymer injection of JZ9-3 oilfield, the composition and characteristics of the blockage in well W are analyzed. A safety depolymerizing agent was developed by the screening and optimization of oxidizer and stabilizer, and the performance evaluation of plugging corrosion, one-dimensional sand-filled pipe model displacement experiments and corrosion rate were carried out. The experimental results showed that percarbonamide can reduce the viscosity rate of high-concentration polymer solutions and gels by up to 99%.After adding a stabilizer, the release rate of active oxygen can be controlled, and it can still maintain 8% active oxygen content at 60℃ after 72 h, which greatly improves the safety of depolymerizer. The blockage removal rate of the depolymerizer is 91.6%, and the permeability recovery rate is 305%. The depolymerizer has the characteristics of low corrosion rate and no oxygen generation, so as to ensure the safety of on-site operation. The application of the depolymerizer in W well shows that it can effectively remove the blockage caused by long-term polymer injection.