The photodissociation of methanol, which is an important radical source on interstellar ices, was studied using quantum chemistry calculations. Surface hopping simulations using the time-dependent density functional theory were performed, and the potential energy curves of the low-lying excited states were analyzed using the second-order multireference perturbation theory to reveal the reaction mechanism in the gas phase. We showed that the generation of CH3O would more frequently occur than that of CH2OH on the S-1 state in contrast to the ground state. We also discuss why the ratio of CH3O and CH2OH differs between the gas and solid phases.