To better understand the initiation and intermediate reaction mechanisms associated with the high-temperature pyrolysis of methylcyclohexane (MCH), the dissociation of MCH is investigated using reactive molecular dynamics (RMD) and density functional theory (DFT) calculations. It is observed that the pyrolysis of MCH is initiated by four types of reaction channels. The initiation of the decomposition is mainly through the C-C bond homolysis of the six-membered ring, leading to ring opening and the formation of C7H14 diradicals. Subsequently, the biradicals undergo successive decomposition by the beta-scission of the C-C bonds to form ethylene. Furthermore, to provide a detailed description of the pyrolysis behavior of MCH, the distributions of key products, intermediate reactions and corresponding kinetic behavior are systematically analyzed at the atomic level. The apparent activation energy extracted from the RMD simulations is 263.60 kJ/mol at temperatures from 2300 K to 3100 K, which is reasonably consistent with the experimental results.