Abstract: Pyrolysis oil and pyrocarbon were prepared from waste tires by pyrolysis. Activated carbon was prepared by activation of pyrocarbon. Ag⁺ modified activated carbon (Ag/AC) was prepared by modifying activated carbon with Ag⁺. Ag/AC was used for adsorption desulfurization of pyrolysis oil. The sulfur compounds in pyrolysis oil were analyzed by GC/MS.The results show that the appropriate temperature and time for adsorption desulfurization of activated carbon were 20 ℃ and 12 h respectively, and the desulfurization rate of unmodified activated carbon was 15.33%, while that of Ag/AC was 38.6%. GC/MS analysis showed that thiophene, 2-methylthiophene, benzothiophene, dibenzothiophene and 4, 6-dimethyldibenzothiophene were the main forms of organic sulfur in the pyrolysis oil, and dibenzothiophene (DBT) had the highest content of 2.57%. The reaction mechanism of Ag⁺ and dibenzothiophene in solution was further explored based on in situ FT-IR, ¹H NMR, ICP-OES and elemental analysis. The results showed that there were two reaction sites on dibenzothiophene molecule: S atom and benzene ring. When Ag⁺ was added into the dibenzothiophene solution, a coordination reaction occured between the Ag⁺ and S atom or the benzene ring on the dibenzothiophene molecule with the coordination number of 1. Two kinds of complexes might be generated during the complexation reaction, and the molecular formulas were Ag(D_S)NO₃ and/or Ag(D_C6H6)NO₃.