We studied the ionization and dissociation of polyatomic molecule methane in an intense femtosecond laser field with wavelength of 810 nm and intensities ranging from 1.4×10^(14) to 2.6×10^(15) W/cm2 by mass spectroscopy. Abundant fragment ions were observed in addition to the strong parent ion. The effect of frequency chirp was investigated and it was found that the negatively chirped pulses dramatically enhanced the dissociation probability, which might be used to control the dissociation pathways.