Abstract: By applying a magneto-optical semiconductor layer of which has the Voigt effect to the surface of a dual-periodical photonic crystal heterostructures doped by impure layer, the transmittance of the defect mode of this photonic crystal makes a response to the external magnetic field.The variation of dielectric constant(refractive index) of the magneto-optical semiconductor surface accompanied with the external magnetic field was studied firstly. And then, the variation of transmittance of the defect mode with a external magnetic field was explored via using transfer matrix method.The results show that under the conditions of selecting a appropriate structural parameters and material parameter, it can realize the correlation between the transmittance of defect mode and the magnetic field,and obtain the transmittance of defect mode controlled by an external magnetic field.Therefore, the photonic crystal with such structure can be applied to the magnetic switch of the narrowband filter.