The main purpose of this paper is to report the high-power laser ionization-dissociation of CH4 at various femtosecond (fs) laser intensities (from 1 x 10 14 W/cm(2) to 2 x 1015 W/cm(2)) with a laser pulse duration of 48 fs. The generalized molecular Keldysh theory has been applied to calculate the ionization yields for CH4+ and CH4++. Outside the influence of the A intense laser, we propose to calculate the mass spectra due to the decomposition of CH4+ and CH4++, using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The agreement between the experimental mass spectra and calculated mass spectra seems to be reasonable.