With the rapid development of consumer electronics, electric vehicles and energy storage, it is urgent to improve the energy density of secondary energy storage devices represented by lithium-ion batteries. Cathode materials are a key issue to improve the energy density of lithium-ion batteries. Li-rich Mn-based layered oxide cathode materials (LRM) are considered as one of the most promising cathode materials for lithium-ion batteries due to their extremely high theoretical specific capacity (>350 mA·h·g-1) and reversible specific capacity (>250 mA·h·g-1). However, the low initial Coulombic efficiency, poor rate performance, and rapid voltage and capacity fading of LRM cathode materials seriously restrict their industrial application. This review introduced the research progress of the crystal structure and electrochemical mechanism of LRM cathode materials, and analyzed the problems of LRM. The modification strategies of LRM cathode materials were comprehensively introduced from the aspects of morphology design control, doping, coating, defect structure design, gradient composition design, layered/spinel heterostructure construction, and electrolyte additives. We provided some ideas and guidance for the future development of LRM cathodes to ultimately promote the practical application of LRM cathode materials.