n order to investigate the electrical conductivity of nano graphite / polyethylene ( PE) composites，the relationship curves between the external electrical filed strength and the electrical conductivity of nano graphite /PE composites with different microstructures are generated based on numerical simulation． The simulation models ofnano graphite / PE composites are designed through changing the contents，diameter to thickness ratio and orienta-tion degree of nano graphite． After a DC electrical field is applied between upper and lower surfaces of the compos-ites，the distribution of electrical current density is calculated based on the finite element method by using theCOMSOL simulating software，and then the electrical current density and the electrical conductivity can be ob-tained． Ｒesearch results indicate the electrical conductivity of the composites increases significantly with the in-crease of diameter to thickness ratio of nano graphite at the same nano graphite content and electrical field strength．As the orientation degree of nano graphite along external electrical field increases，the electrical conductivity of the composites obviously increases． It can therefore be concluded that change of the microstructures of nano graphite /PE composites is effective to control the electrical conductivity of the composites．