Photoisomerizations of 6-hydroxy-5,12-naphthacenequinone and its derivatives bearing methyl and phenyl group were theoretically investigated with den-sity functional theory and ab initio CIS method at the B3LYP 6-31G basis set, respectively. The obtained poten-tial energy curves revealed that a four-state cycle existed in the ground and excited states. It was also found that the activation energy for the methyl transfer was higher com-pared to that for the phenyl transfer, and this was consistent with the experimental results that the photoisomerization of the phenyl substituted derivative was more rapid than that of the methyl substituted derivatives. Further hybrid time-dependent density functional theory (TD-DFT) was used to investigate the absorption and fluorescence spectra of these compounds under solvent effect condition. The calculated values were in agreement with the experimental results and the excitation condition of photochromic reactions.