Ultra-high temperature ceramics and their composites have become the focus and frontier of thermal structural materials research in the field of aerospace because of their advantages of ultra-high temperature resistance, lightweight and anti-oxidation ablation. Based on the excellent performance and successful application of rare earth compounds in thermal barrier coatings and other fields, researchers have introduced rare earth compounds into ultra-high temperature ceramics and their composites to improve the structure and properties of oxide layer in order to solve the problems of rapid growth of oxide layer of ultra-high temperature ceramic matrix composites and easy spalling of high and low temperature circulating oxygenation layer in a wide temperature range. This paper summarized the research status of rare earth modified ultra-high temperature ceramics and their composites, analyzed and discussed the modification mechanism, and looked forward to the future research and development direction.