Au film is mainly used to prepare the metal structure of the terahertz (THz) microstructure. When the metal structure is fixed, it is difficult to control the terahertz wave by using the properties of Au film. In this paper, the tera-hertz microstructure based on the soft magnetic FeNHf film with the high permeability is designed and fabricated on the high resistivity silicon substrate. The magnetization direction of soft magnetic film is controlled by the external magnetic field H. The THz transmission characteristics and electromagnetic resonance mode of the microstructure under the control of H in split triangular structure are systematically studied. The soft magnetic FeNHf film has the characteristic of magnetic anisotropy. Therefore, the direction of the magnetization M in FeNHf film can be controlled by the external magnetic field H to be perpendicular and parallel to the magnetic field of THz wave, respectively. The THz time domain spectroscopy system is used to test the terahertz transmission characteristic of the microstructure. The finite difference time domain method is used to analyze the THz electromagnetic field distribution and modula-tion mechanism based on the microstructure of the FeNHf film. The experimental results show that the resonance frequency of the split triangular THz microstructure can be modulated under magnetic field. At the frequency of 1.3 THz, the tunability and modulation depth are about 5.7% and 15%, respectively.