Abstract: The common gear fault types are summarized. The principle of acoustic emission technology for gear detection and monitoring is introduced. Research and application of acoustic emission technology in gear fault detection are reviewed, including the mechanism study, the influence of operating conditions on the acoustic emission signals and the acoustic emission signal processing technology. The research progress of various signal processing methods in gear fault diagnosis are especially analyzed. Potential problems and future research directions of acoustic emission technology in fault diagnosis research, which have reference significance for peer.