Abstract: The mechanism of the degradation of ibuprofen by UV/H₂O₂ was studied by establishing a pseudo-first-order reaction kinetics model based on steady-state hypothesis. The results show that UV/H₂O₂ synergistic degradation of ibuprofen has higher degradation efficiency compared to only UV or only H₂O₂ alone, because ^·OH plays a major role in UV/H₂O₂ systems. At the initial conditions of pH=7,IBU₀=10 μmol/L,H₂O₂₀=600 μmol/L, the steady state concentration of ^·OH in the system is 1.54×10^-12 mol/L, The secondary reaction rate constant of IBU and ^·OH is 5.51×10⁹ L·mol^-1·s^-1.