Molecular dynamics simulations were performed on the relaxation of fully extended polyethylene chains, varying in length from 600 to 4000 CH2 units. When a chain has more than 1200 CH2 units, the relaxation proceeds in three stages, subglobule formation, subglobule growth, and subglobule coalescence into one globule. In the stage of subglobule growth, the number of subglobules is almost a constant because of kinetic barrier, which is different from the results based on Monte Carlo simulations of polymer collapse in dilute solution. The difference of lamella thickness between MD simulations and experiments is discussed. The degree of adjacent reentry is calculated, and amounts between 0.4 and 0.5 for the formed lamellae.