As duplicated cases of ultrathin polymer films,multilayer nanostructures are of great interests in various applications.Coarse-grained molecular dynamics simulations were carried out to understand the microstructure of multilayer films.The multilayer polymer films have structural heterogeneity with the chains near the interfaces orienting perpendicularly to the normal,while it is bulk-like in the central region of each layer,so the enhancement of mechanical properties of multilayer nanostructure is due to the increase of the number of interfacial layers and the chain orientation.Samples of graphite/polypropylene composites with different layers and particle sizes were prepared by micro-layered extrusion device.The crystallinity,mechanical and dielectric properties of the samples were measured by related testing machine.These data are also compared with the results of molecular simulations.With the same amount of graphite addition,the tensile strength of composites increases with the number of interfacial layers,but decreases with the increasing of the particle size,and the longitudinal tensile strength is greater than the transverse one.That is because chains near the interfaces transform from curling state to extended state with order and compact arrangement.Graphites near the interfaces could be aligned in a plane in the polymer matrix by multilayer extrusion.This could provide the possibility of two-dimensional reinforcement in the plane of orientation.The crystallization temperature of composites increases with the number of layers and the crystallinity increases linearly.That is because the increase of the number of layers could improve the orientation induced crystallization.The dielectric constant has a small increase and the dielectric loss has no change.That is because graphites in the matrix aligned in parallel with each other with the formation of micro capacitance structure.This work would be helpful for the optimization of extrusion process in future.