Abstract: The experiment uses vacuum ultraviolet (VUV) as the light source，the reaction mechanism and transformation pathway of rhodamine B (RhB) degradation bypotassium monopersulfate (PMS) catalyzed by VUV and Co²⁺were studied.Under the initial mass concentration of RhB of 80 mg/L, Co²⁺and PMS of 15 umol/L and 0.5 mmol/L respectively, the RhB removal rate can reach 99.1% after 10 minutes of reaction in the VUV/Co²⁺/PMS system. The degradation of RhB in the VUV/Co²⁺/PMS system follows a first-order kinetic law, R²>0.990. The reaction rate constant (k) decreases with increasing initial mass concentration; The pH value of the solution has a significant impact on the reaction rate, and the lower the pH value, the slower the rate. HCO₃^- and Cl^- with a concentration of 30mmol/L showed significant inhibitory effects,compared to the control group at 10 minutes ,and the RhB removal rates decreased to 66.0% and 84.2%, respectively; NO₃^- and SO₄^2- have only a slight inhibitory effect; the printing and dyeing additive sodium citrate also significantly inhibits RhB degradation.The free radical capture experiment and electron paramagnetic resonance (EPR) test results indicate that the oxidized species present in the VUV/Co²⁺/PMS system include sulfate radical , hydroxyl radical, and singlet oxygen. Based on the UV visible absorption spectrum and intermediate product analysis results, the possible conversion pathways and reaction mechanisms of RhB during the degradation process were proposed.After testing TOC, the mineralization degree of RhB can reach 43.8% at 30 minutes.