Practical application of Human robot interactions (HRI) has made great progress, but the performance of HRI robot equipment is still limited by the robotic joint reducer. It is sorted out about the research of domestic and foreign scholars on robot joint reducers, especially for the mainstream technologies of common robotic joint reducer such as planetary gear transmission, harmonic transmission, cycloidal pinwheel transmission and RV transmission technology. So the structure characteristics, transmission mode, the advantages and disadvantages are compared and described. Applicability and performance analysis framework of robotic joint reducer is proposed. Then two new transmission technologies of gear bearing transmission and Galaxie drive are introduced according to the future development trend of robots. And the future technology of the robotic joint reducer is prospected, so as to provide reference for the design and selection of robot joint reducer.