The DC distribution grid can access friendly various types of distributed power supplies and DC loads. It is an effective means to deal with energy crisis and environmental pollution by forming AC-DC hybrid distribution grids with existing AC distribution grids. However, the lack of reliable and stable relay protection technology is an important factor that restricts the development of hybrid AC/DC distribution grids. The purpose of this paper is to outline the research status of relay protection for domestic and foreign DC hybrid power distribution grids. It summarizes the research on the structure, fault characteristics and protection principles of DC distribution grids, and then analyzes the fault characteristics of AC/DC hybrid distribution grids and the influence of AC-DC interactions on the protection configuration. At the same time, the research on the relay protection of AC/ DC converters is summarized. Finally, the research direction of relay protection technology for AC/DC hybrid power distribution grid is prospected. This work is supported by National Key Research and Development Program of China (No. 2017YFB0903205) and Science and Technology Plan of Guangdong Province (No. 2017A010104023).