Abstract: Currently, the flexible Direct Current（DC） grid usually adopts the half-bridge Modular Multilevel Converter（MMC）, and it has basic characteristics such as low inertia and small damping. The technical challenges including rapid fault development, weak overcurrent tolerance and insufficient current breaking ability should be carefully addressed. It is of significance to properly handle the fault current limiting issues of the flexible DC grid. In this paper, the development requirements of flexible DC transmission technology and the necessity of introducing fault current limiting approaches are stated. Domestic and foreign research results are systematically summarized. According to the classification of the actual and virtual fault current limiting schemes, their technical advantages and disadvantages are compared and analysed. Finally, the probable development direction of the fault current limiting approaches for the flexible DC grid based on half-bridge MMC are suggested, and potential problems as well as solutions are discussed.