By using the first-principles method based on the density-functional theory, the spin transport properties for the systems consisting of iron-doped zigzag-edged graphene nanoribbons (ZGNRs) with iron doping at the interface, where the connection is realized between electrodes and the central scattering region, are investigated theoretically. The ribbon widths of ZGNRs are four zigzag C chains (4 ZGNRs), and the length of scattering region is N unit cells (here, N=4, 6, 8, 10). Results show that -spin current is obviously greater than the -spin current under the ferromagnetic (FM) configuration, which is the spin filtering effect. The reason of spin filtering effect cames from two aspects: a) The symmetry-dependent transport properties which arise from different coupling rules between the up and * subbands around the Fermi level, that are dependent on the wave-function symmetry of the two subbands; b) the distribution of molecular orbit within the bias windows, location, or delocalization. While for antiferromagnetic (AFM) spin state, both and spin currents are very small and both the positive and negative bias regions originate from the existence of band gap; therefore, no obvious spin filtering effect can be obtained. For antiparallel (AP) magnetism configuration, spin filtering effect also can be obtained at high bias. Next, we also investigate the other models: the ribbon width of ZGNRs is five (six) zigzag C chains, namely, 5 ZGNRs (6 ZGNRs), and the scattering region is 6 unit cells length. The currents in 6 ZGNRs are less than that of 5 ZGNRs obviously, and this difference is revealed to arise from different couplings between the conducting subbands around the Fermi level, which is dependent on the symmetry of the systems. However, both of the two models show the similar characteristic: spin filtering effect. The spin current is obviously greater than the -spin current with the whole bias under the ferromagnetic (FM) configuration, The analysis on the electronic structure, transmission spectra, the molecular projected self-consistent Hamiltonian (MPSH) which have been modified by the electrodes, local density (LDOS) and the spin density give an insight into the observed results for the systems. These results indicate that the iron doping at interface between electrodes and central scattering region for ZGNRs can modulate effectively the spin electrons. It is of important significance for developing high spin polarization filtering device based on GNRs.