Bolt connection is widely applied in aerospace structures. The bolted state of the structure is directly related to the safety and functionality of the equipment. The aircraft is faced with a variety of extreme environments such as vibration and impact in service

which will eventually lead to the phenomena of loose and slip of the bolted joints. Therefore

it is of great significance to monitor the connection state of the structure. This paper mainly reviews the research status and testing principle of bolt connection state testing technology. Firstly

the research status of bolted state mechanism is analyzed

which mainly includes the theory of joint surface microscopic characteristics and the theory of structural nonlinear dynamics. Then

the traditional direct measurement techniques of the bolted state are introduced

and its measurement accuracy and application limitation are analyzed. Finally

the principles of various types of the bolted state testing technologies based on response signals are reviewed

including vibration signal analysis method

electromechanical impedance method

acoustic elastic effect method

ultrasonic energy method and FBG sensor method. Their advantages

disadvantages and application range of the method are analyzed and the development direction is pointed out.