Human robot interactions has been widely used in various fields,but the performance of robot is still limited by the robotic joint reducer technology when interacting with humans.By combing 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 pin wheel transmission and RV transmission technology,the structure characteristics,transmission mode and the advantages & disadvantages were compared and described.The applicability and performance analysis framework for robotic joint reducer was proposed.Two new transmission technologies of gear bearing transmission and Galaxie drive were introduced for future robot application scenarios,and the development trend of robot joint reducer technology was forecasted,which provided reference for the design and selection of robot joint reducer.