Abstract: According to the relationship between the ultrasonic velocity and the internal stress of the material in the theory of acoustic elasticity, a method of measuring the axial stress of the fastening engine bolt by using the integrated longitudinal and transverse wave probe is proposed. The measurement coefficient of axial stress of bolts with different materials under high load is studied and the calibration method of bolt material coefficient is given. This paper mainly analyzes the measurement results of engine cylinder block and bearing high strength bolts during loading to about 140 kN. The experimental results show that the error range of ultrasonic stress measurement is within 5 kN.