With the rapid increase of wireless devices and the openness of wireless communication, the security problem becomes more and more serious and challenging. Different from traditional key-based cryptography schemes, physical layer security has been proposed to realize unconditional security from the information theory perspective. This paper provides a review of the model of physical layer security built by Shannon and tracks the evolution of security schemes without key leaded by Wyner and secret key-based secrecy schemes leaded by Maurer. Among them, the former aims at widening the channel quality gap between the authorized user and the eavesdropper; while the latter using the wireless channel as a nature random source exploiting the channel characteristics. In the coming fifth generation mobile communication scheme, physical layer security can match it with a lightweight security technology which avoids the long delay in the traditional cryptography. Although the theoretical studies of physical layer security have become maturity, they still face many practical problems to be solved in practical.