Abstract: Fenton-ultraviolet irradiation(Fenton-UV) combined process was used to treat ultra-high-concentration polyvinyl alcohol(PVA) organic waste liquid of nuclear power plants, and the changes of PVA conversion rate, average molecular weight, solution viscosity, etc. over time were studied. The results show: for 50 g/L PVA solution, the concentration of H2O2 is 15 g/L, the concentration of FeSO₄·7H₂O is 0.050 g/L, the initial pH is 3, after 2 h Fenton reaction followed by 2 h UV irradiation(3 mW/cm2), the removal efficiency of PVA reaches 100%, and the average molecular weight in solution decreases from 60 000~80 000 Da to <1 000 Da. The viscosity decreases to 1.1 mPa·s, while only slight variations are observed for total organic carbon and COD. Fenton-UV method can be used as a pre-treatment. In the former Fenton stage, the solubility increases, and the concentration of PVA in solution can reach a very high level. A preliminary degradation and oxidation are also conducted in this stage. During the later UV stage, PVA can be further degraded, and the molecular weight and viscosity are significantly decreased. Fenton-UV treatment will be benefit to the further treatment, and it can be a cost-effective treatment method for ultra-high concentration PVA solution.