Abstract：This paper provides a review of the development in physical layer security in the recent 20 years and focuses on tracing the evolution of the secret key-based mechanism of physical layer security. The essence of this secret key generation method is to generate a group of secret keys between the sender and the receiver via communications over a public and error-free feedback channel. Meanwhile, the reciprocal nature of radio channel provides the possibility to use this key generation mechanism in this field. According to the procedure of the secret key generation method, we first analyze the channel measurements step combined with real application scene from the perspective of validation of reciprocal, measurements compensation, channel characteristics and décor-relation. Then, we discuss the theoretical foundation of this secret key-based scheme and compare its advantages and disadvantages over different channel characteristics, quantization, and information reconciliation and privacy amplification strategies. Finally, this survey concludes with observations on potential research directions and challenges with the development of the fifth generation mobile communication in this area.