Abstract: Based on Halbach array permanent magnets and the magnetic field demand of optical isolator, two permanent magnet systems for high power isolator are presented. The magnetic field distribution characteristics and the effect of magnetic field inhomogeneity on isolation are analyzed. The magnet assembly error is also discussed. The results show that, the use of oblique magnetization magnet can increase the magnetic field intensity and drastically reduce the required magnetooptic crystal length of Faraday rotator. And the isolation affected by magnetic field inhomogeneity is related to magneto optic crystal aperture, length and the incident laser beam radius, it can be significantly improved by reducing crystal radius and beam radius while magneto-optic crystal length is fixed. The isolation degree is 105.8 dB and 45.4 dB respectively for the proposed two permanent magnet systems, when the radius of incident light is 1.5 mm and magneto-optic crystal radius is 5 mm.