The definition of physical human-robot interaction is introduced, the injuries for human from the interaction processing are analyzed, and the safety assessments are given. Then, it summarizes the safety strategy used in the physical human-robot interaction. Furthermore, it presents the research progress in the physical human-robot interaction and highlights the questions and challenges in this field on the basis of analysis and research mentioned above. This paper points out that the injuries analysis and safety assessments of physical human-robot interaction mainly focus on the blunt/sharp collision caused the bones and soft tissue injury currently, and lack of study on organs, blood vessels, nerves, and other injuries. Collision avoidance, wrapped in soft elastic material and compliant joint design are the main safety policy. By comparing design ideas and construction schemes of these methods, it summarizes the advantages, disadvantages and main problems. It suggests that the combination of cognitive human-robot interaction and physical human-robot interaction will be the developing direction to enhance the safety of the latter because a single means or a strategy can not guarantee the safety of human-robot interaction.