With the rapid development of optical communication technology and the improvement of laser average power, magneto-optical isolators are required to ensure the unidirectional propagation of light, thereby maintaining the stable and efficient operation of the optical system. As the core component of optical isolators, magneto-optical medium has also developed rapidly. Several magneto-optical materials and the shortcomings of the current magneto-optic garnet crystals, as well as the principle and application of the Faraday effect are first briefly introduced. Then, the advantages and disadvantages of the current various fluoride magneto-optical crystals as a new generation of magneto-optical crystals are systematically analyzed. Finally, the potential application of CeF₃ magneto-optical crystals and the future development of fluoride magneto-optical crystals are prospected.