► Mechanical properties of graphene are investigated via MD simulations. ► Effects of different layer numbers, temperatures and isotopes are considered. ► Temperature exerts negative effect on the mechanical properties. ► Layer number and isotopes pose marginal influence on the mechanical properties. Herein the mechanical properties of graphene, including Young’s modulus, fracture stress and fracture strain have been investigated by molecular dynamics simulations. The simulation results show that the mechanical properties of graphene are sensitive to the temperature changes but insensitive to the layer numbers in the multilayer graphene. Increasing temperature exerts adverse and significant effects on the mechanical properties of graphene. However, the adverse effect produced by the increasing layer number is marginal. On the other hand, isotope substitutions in graphene play a negligible role in modifying the mechanical properties of graphene.