A magnetic field detection micro-cavity model based on parity-time (PT ) symmetry structure is proposed.Using the magnetic-optical effect of hydro-b as ed Fe₃O_4magnetic fluid medium layer and the optical amplification effect of t he PT-symmetry structure,when the magnetic field strength changes,the defect mo d e position in the structure band gap is changed.Therefore,the magnetic field i ntensity can be detected by detecting the defect mode position.In this paper,t he 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 in tensity in the PT-symmetry element are numerically optimized.The optimized sim u lation results show that the sensor can achieve effective magnetic field intensi ty detection,the sensitivity of the sensor can reach 97.14nm/RIU in the magnet ic field intensity range of 0—500Oe,the figure of merit and detection limit ca n reach 10^4and 10－7 RIU,respectively.Meanwhile,the resolution value ca n be a s low as 0.05Oe and as high as 2Oe.The proposed sensor structure can be used in the design of high comprehensive performance magnetic field intensity testing equipment.