Arylazoimidazoles are a series of azobenzene, derivatives possessing the ability to undergo photoinduced trans-cis isomerization. Their isomerization quantum yields are found to be dependent on the excitation wavelength and chemical substituents. The current work investigated the ultrafast nonadiabatic decay behaviors of three arylazonnidazoles (Pai-H, Tai-H, and Tai-Me) after being photomited to the S-1 and S-2 states by means of high-level ab initio potential energy calculations and, on-the-fly surface hopping dynamical simulations in gas phase to explore the effect of the methylation. The results found that the Pai-H with no methylation substituents only decay along a NNC bending reaction pathway for both the. S-1 and S-2 states. The Tai-H with a methylation substituent on the six-membered ring can decay along both the NNC beriding and twisting motion pathways for. the S-1 and S-2 states. The Tai-Me has methylation substituents on both the six- and five-membered rings prefers to decay by a twisting motion in the S-1 state, while a NNC bending channel is activated following excitation to the S-2 state. The position and numbers of methylation substituents has important influence on the dynamical behaviors of arylazoimidazoles The current work provides fundainental knowledge of the arylazoimidazoles and will be helpful for advanced and further exploration and application.