With hydrotreated diesel oil as raw material,the separating properties of MgY aromatic adsorbent in simulate moving bed reactor was investigated.After running a long cycle of 830 d,the mass fraction of aromatic in product decreased from 98.6% to 84.7%,while the mass fraction of non-aromatic components increased from 1.3% to 7.8%.The separation performance was significantly reduced,and the adsorbent was inactivated.The deactivated adsorbent was characterized by UV-Vis,NH₃-TPD and TGA.The framework structure of deactivating agent was decomposed by hydrofluoric acid solution of 40% （mass fraction）,through the ultrasonic extraction carbon tetrachloride was added for extracting deactivated substances,the types of deactivation substance were analyzed by X-ray diffractometer（XRD） and GC-MS.The deactivated substances were mainly C₁₀~C₁₆ aromatics,including aromatics with side chains,double ring or tricyclic aromatic hydrocarbons.As the reaction progresses,the aromatic hydrocarbon on the adsorbent accumulated continuously,leading to the polar position being covered and deactivation,but there was no obvious carbon deposition on the adsorbent.Non-aromatic hydrocarbon/aromatic hydrocarbon separation of adsorbent recovered basically after regeneration at 450 ℃,adsorption-desorption process tended to equilibrium.