A magnetic field detection micro-cavity model based on parity-time (PT) symmetry structure is proposed.Using the magnetic-optical effect of hydro-based Fe3O4 magnetic fluid medium layer and the optical amplification effect of the PT-symmetry structure,when the magnetic field strength changes,the defect mode position in the structure band gap is changed.Therefore,the magnetic field intensity can be detected by detecting the defect mode position.In this paper,the transmission spectrum of the structure is theoretically analyzed based on the transfer matrix method (TMM),and the parameters such as the structure period,the thickness of the dielectric layer and the macroscopic Lorentz oscillation intensity in the PT-symmetry element are numerically optimized.The optimized simulation results show that the sensor can achieve effective magnetic field intensity detection,the sensitivity of the sensor can reach 97.14 nm/RIU in the magnetic field intensity range of 0—500 Oe,the figure of merit and detection limit can reach 104 and 10－7 RIU,respectively.Meanwhile,the resolution value can be as low as 0.05 Oe and as high as 2 Oe.The proposed sensor structure can be used in the design of high comprehensive performance magnetic field intensity testing equipment.