Based on the full wave scattering theory，we establish the effective media theory for the composite system，where graphene-coated nanowires are parallel to each other and randomly embedded in the host medium.Under the long-wave limit，we achieve the equivalent (EQ) permittivity and permeability of the graphene-coated dielectric (GCD) nanowire，and we demonstrate that the far-field scattering spectrum of the electromagnetic structure with equivalent parameters matches well with the one of the composite system. Besides，we find that it is possible to realize tunable invisibility and resonance by varying the permittivity of the dielectric nanowires or the chemical potential of the coated graphene. With further study，we prove that there also exists tunable Fano-resonance in such composite system.