Physicallayer authentication technology is a new type of identity authentication in recent years． It embeds identity authentication information in the wireless communication signal of physical layer， so as to realize identity authentication in physical layer． On the one hand， this technology can achieve authentication，with transparency of upper layer protocol，and lower overhead of upper layer protocol; on the other hand， it can avoid identity authentication attacks for highlevel protocols and improve system security． This paper introduces two key technologies of physical layer authentication: radiofrequency fingerprint and radiofrequency watermarking． Then，a unified classification system for the proposed methods in the present literature is established， the advantages and disadvantages of the existing schemes are investigated，and，finally，the future development direction in this field is discussed．