Molecular dynamics simulation was performed to study the diffusion mechanism of n-alkanes C1—C4 in copper（Ⅱ） benzene-1,3,5-tricarboxylate（Cu-BTC）. The self-diffusivities of n-alkanes were calculated, and the diffusion paths of different types in the main and second channels were discussed by means of center of mass probabilities and trajectories. The simulation results indicate that the diffusion of various n-alkanes in Cu-BTC follows their preferential paths, which have distinct diffusion resistance, leading to the difference in diffusivity. The information obtained provides a better understanding of the diffusion of n-alkanes in metal-organic frameworks（MOFs）, as well as to guide the practical applications and future design of new MOFs.