Abstract: Quantum secure direct communication is a communication model that directly transmits secret information in the quantum channel.It has changed the structure of secure communication from a two.channel structure with key distribution and ciphertext transmission to a single.channel with one quantum secure direct communication.This reduces the security loopholes and improves the security.It also develops the theory of communication, from reliable communication in the noisy channel, which is guaranteed by Shannon爷s theory, to secure and reliable communication in the noisy and eavesdropping channel, guaranteed by Wyner爷s wiretap theory.This paper introduces the principles and characteristics of quantum secure direct communication, reviews the specific steps of two typical protocols of quantum secure direct communication, surveys the important experimental progress in recent years, and gives the future prospect of QSDC.

Key words: quantum secure direct communication, secure communication, quantum key distribution, quantum communication