In order to research the magnetic field interference on cables nearby 3phase air core reactor and the shielding effect of different materials, this paper analyses the influence of high conductivity materials and high permeability materials on spatial magnetic field on the basis of 3D electromagnetic field simulation model. Then the influence mechanisms are expounded. Furthermore, the induced voltages in different shielding measures are calculated and discussed basing on magnetic vector potential obtained from the finite element simulation results. The results show that, for the shielding of high permeability materials, good shielding effect can be achieved only by connecting 3 phases shield together. Moreover, a large number of magnetic leakages on the edge of shield may aggravate the magnetic field interference in surrounding areas. Therefore, the distribution of onsite cables in substation needs to be considered when applying high permeability 3phase connection shielding.