Magnetic fluids are the suspensions composed of magnetic nanoparticles, surfactants, and non-magnetic carrier liquids. Magnetic fluids are widely used in various fields, especially in sealing, because of their excellent features, including rapid magnetic response, flexible flow ability, tunable magneto-viscous effect, and reliable self-repairing capability. Here, we provide an in-depth, comprehensive insight into the theoretical analyses and diverse applications of magnetic fluids in sealing from three categories: static sealing, rotary sealing, and reciprocating sealing. We summarize the magnetic fluid sealing mechanisms and the development of magnetic fluid seals from 1960s to the present, particularly focusing on the recent progress of magnetic fluid seals. Although magnetic fluid sealing technology has been commercialized and industrialized, many difficulties still exist in its applications. At the end of the review, the present challenges and future prospects in the progress of magnetic fluid seals are also outlined.

磁性流体是由磁性纳米颗粒、表面活性剂和非磁性载液组成的悬浮液。磁性流体因其磁响应快、流动能力灵活、磁粘效应可调、可靠的自修复能力等优异特性而被广泛应用于各个领域，尤其是密封领域。在这里，我们从静密封、旋转密封和往复密封三类，深入、全面地介绍了磁流体在密封方面的理论分析和多样化应用。我们总结了从 20 世纪 60 年代至今的磁流体密封机理和磁流体密封的发展，特别重点介绍了磁流体密封的最新进展。虽然磁流体密封技术已经商品化、产业化，其应用中仍存在诸多困难。在回顾的最后，还概述了磁流体密封目前的挑战和未来的发展前景。