In this study, simulation of ab initio molecular dynamics with phonon spectral analysis was performed with the aim of understanding the two-dimensional thermal conductivity in graphene. Using the atomic velocities obtained from the simulation of ab initio molecular dynamics, and the analysis of spectral energy density, we calculated the lifetime of phonons in each mode. The calculations show that acoustical phonons ZA, LA and TA phonons have larger lifetimes and mean free path so they have more contribution in thermal conductivity. Among optical phonons, ZO-mode phonons, i.e. vibrations perpendicular to the graphene layer, have a longer lifetime than LO, TO models, but due to the low group velocity, their role in thermal vesting is negligible.