Molecular dynamics (MD) studies are carried out to investigate the electron irradiation damages in carbon nanomaterials. The interaction between an incident electron and a carbon atom is modeled based on the Monte Carlo method using the elastic scattering cross section. The electron irradiation damages in graphen, graphite, single-walled carbon nanotube (SWNT) and carbon nanopeapod are demonstrated. The cross-links among the nanostructures caused by the knock-on effect are observed as typical damages. The dependence of the damages on the electron primary energy is also shown for the SWNT.