Abstract: For the detection of the axial stress of bolts, the theoretical and experimental research on the propagation characteristics of ultrasonic body waves was carried out. Based on the acoustoelastic effect, the influence of axial stress on the longitudinal and transverse wave velocity and length of the bolt was theoretically analyzed. At the same time, a mathematical model of the combination method of longitudinal and transverse waves was proposed to realize the accurate measurement of bolt axial stress. The ultrasonic signal excitation acquisition hardware circuit was designed, and the corresponding host computer software was developed to build an ultrasonic system for bolt group stress detection. The characteristic parameters of longitudinal and transverse waves of grade 10.9 carbon steel bolts with a size of M24×100 (thread diameter×length, mm) were extracted experimentally. The results showed that the average error rate between the measured stress value and the actual stress value of the selected carbon steel bolts was less than 5%, which met the needs of actual working conditions.