Abstract: Using the B3P86 method of density functional  theory and timedependent density functional theory (TD-DFT), we calculated excitation energies, wavelengths and oscillator strengths of 2-methylcyclohexanone (CH₃—C₆H₉O) molecules from ground state to the excited states of 1—8 at the 6-311++g(2-df-) basis sets, and studied the influence of the excited states of CH₃—C₆H₉O molecules under different external electric fields. The results show that the excitation energies of the excited states S2,[KG-*3]S3,[KG-*3]S4,[KG-*3]S5,[KG-*3]S8 of CH₃—C₆H₉O molecule decrease sharply with the increase of external electric field intensity. The CH₃—C₆H₉O molecule can be easily excited and dissociated under the action of external electric field.

Key words: 2-methylcyclohexanone, excited state, timedependent density functional theory (TD-DFT), electric field