As a key point to applying and studying magnetic photonic crystal technology, communication devices such as the magnetic photonic crystal filters with high performance and easy integration are developed. We investigate the feasibility of ferrite magnetism materials that can be used to make photonic crystal filters. The optical properties of the magnetic materials may be tuned by adjusting the magnetic field or temperature. The band gap of the magnetic photonic crystal can thus be transferred by changing the external magnetic field. This kind of magnetic photonic crystal has a great application prospect. A low insertion loss and narrow-band filter is designed based on a magnetic field-controlled ferrite defect in a photonic crystal for a terahertz (THz) wave. Ferrite is a ferromagnetic metal oxide with high dielectric constant, low saturation magnetization intensity, and high magnetic permeability at high frequencies. According to the crystal structure it can be divided into three categories: spinel, garnet and magnetic rock types. The garnet ferrite crystal can be used to realize THz band transmission, and its absorption coefficient is low (0.05-0.3) in uniform polarization. In this paper, a novel magnetic THz photonic crystal filter is proposed, in which point defects are produced by the introduction of garnet ferrite magnetic materials. Based on the coupling characteristics between the linear defect wave guide and the point defects, THz wave with a certain wave length can be well coupled by changing the radius and arrangement of the resonant cavity, so as to achieve high efficiency filter function. The permeability properties of ferrite magnetic materials are changed with the variation of the intensity of the external magnetic field, and the tuning of the frequency of the resonance mode. The optical properties of the filter are analyzed in detail by using plane waves method(PWM) in finite difference time domain(FDTD). Simulation results show that by changing the point defect structure and the radius of a certain dielectric cylinder, the insertion loss and 3 dB bandwidth of the filter are 0.0997 dB and 8.22 GHz, respectively.