Abstract: The ultrasonic wave was used to detect the bolt stress, and the linear relationship between the ultrasonic time difference and the stress was deduced theoretically. Through the calibration test of the relationship between acoustic time difference and stress of brake bolts, the material coefficients of the same type of bolts can be obtained. The method of on-line and real-time detection of bolt axial stress in wind turbine is proposed, and the man-machine dialogue is realized through the remote upper computer design operation interface, and the whole process of bolt stress detection and warning is completed.