Abstract: To address the difficulty of oil-water separation caused by high viscosity and strong emulsion stability of polymer-containing wastewater, a non-equilibrium plasma reactor with dielectric barrier discharge (DBD) configuration was constructed, and oil-water separation experiments were carried out on simulated polymer-containing wastewater. The effects of solution concentration, oil–water volume ratio, discharge voltage, treatment time, and electrode configuration on oil removal behavior were systematically investigated, and the separation mechanism was analyzed in combination with changes in solution viscosity and water quality parameters. The results show that under the conditions of an HPAM concentration of 1 g/L, an oil–water volume ratio of 1:100, a peak discharge voltage of 30 kV, a single-electrode configuration, and a treatment time of 12 min, the oil removal efficiency can stably exceed 99%. During plasma treatment, the solution viscosity decreases from 180.7 mPa·s to 58 mPa·s and exhibits a strong correlation with oil removal efficiency. Mechanistic analysis indicates that non-equilibrium plasma regulates the structural characteristics of polymer-containing wastewater through the synergistic effects of oxidative reactions and ionic environment modulation, resulting in viscosity reduction and consequently achieving efficient oil–water separation.