There are still some recalcitrant and toxic substances contained in the papermaking wastewater after the biological treatment, so it is necessary to conduct advanced treatment. This paper designed the types and modified methods of fly ash, and then utilized the orthogonal test and single factor analysis to determine the influence of various factors and the combination of optimal levels of Photo-Fenton method of modified fly ash. The results show that the acid modified fly ash has great synergistic catalytic effect. The optimal reaction conditions of papermaking wastewater treatment using the method without adjusting the pH value of raw water are shown as follows: the dosage of fly ash is 34g/L, the dosage of H2O2 is 8.2mmol/L, the dosage of FeSO4·7H2O is 8.8mmol/L and the reaction time is controlled in 45min.In this case, the removal efficiency for COD can reach 71.72%.