Abstract: Audio information hiding technique has become one of the research hotspots in recent years. With such techniques we may embed secret information into audio files, so as to get'covet communication' and 'copyright protection' etc. At first, this paper describes some basic items as human auditory system, formats of audio file, transmission environments of audio signal, and some basic requirements for audio information hiding as well. Then it focuses on the principles and limitations of those audio information-hiding techniques presented so far. At last it points out some promising directions in this research area.