The present paper is devoted to the calculation of transition wavelengths, os cillator strengths f, Einstein An0 and B0n coefficients of methane from ground state Ｘ～lＡl to the first six di fferent excited states by employing density functional theory and single substitute con figuration interaction (CIS) approach with basis sets 6-311++G**. At the same time, the excited states of methane under an external electric field are i nvestigated. It is shown that the total energy of the system has little change d, and simultaneously the HOMO-LUMO gaps become small and the Fermi levels dec lines slightly as the external electric field intensity become strong. The trans ition between ground state Ｘ～lＡl and the high-excited state of methane is easy bring about.