A theoretical study on the geometries, reaction paths, as well as the frontier molecular orbitals of the ozone oxidation of benzothiophene and its derivatives was conducted by using the density functional theory B3LYP method at 6-31G* and 6-311++G(d, p) levels. Firstly, ozone attack on the double bond of benzothiophene (BT). The highest occupied molecular orbital (HOMO) of the ozone and the lowest unoccupied molecular orbital (LUMO) of benzothiophene are symmetrical matched each other to generate a complex. Finally, 2-mercapto-benzoic acid was produced by breaking the double five-membered ring. Furthermore, the ozonation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) are calculated. The sulfides were oxidized to sulfoxide, and further oxidized to sulfone. Based on the activation energies, the reactivity of benzothiophene and its derivatives to ozone are in the following order: BT > 4,6-DMDBT > DBT.