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On the basis of density functional theory and its time-dependent extension,the S0→S1 absorption spectrum of phenanthrene and naphthalene were simulated using the Franck-Condon(FC)approximation including the Herzberg-Teller(HT)and Duschinsky contributions to electronic transition dipole moments.When compared the FC spectrum with the FCHT one,it can be found that the HT effect was more dominant than the FC contribution(calculated spectra were shown in Fig.1).The HT and Duschinsky mixing were also considered in this paper,the pure HT(named HT)and the summation of HT and Duschinsky mixing(named HT)were presented separately.When compared HT with HT,it can be found that the strength of the vibration modes were redistributed distinctly(as shown in Fig.2).Moreover,the anharmonicity[1] was taken into account and the result showed that the effect of first-order anharmonic correction is unconspicuous.Further more,we have tentatively assigned the vibrational lines in the simulated absorption spectrum and the theoretical result matched well with the optical spectrum obtained by experimental[2] observation except that the intensity of several vibronic bands were underestimated(experimental and simulated spectra were presented in Fig.3).The present work has provided a suitable method to simulate the absorption spectrum of phenanthrene and naphthalene.We expect the method could be a guideline for the further study of the other cata-condensed aromatic hydrocarbons.