The acoustoelastic effects of ultrasonic longitudinal and transverse waves in 45 # medium carbon steel with three different crystal structures processed by different heat treatment processes were analyzed. The results show that the sensitivity of ultrasonic longitudinal wave is better than that of transverse wave in bolt stress measurement, and the crystal structure of the material has a great influence on the linearity and repeatability of the acoustoelasticity, which can be improved by increasing the number of stress strengthening cycles. Among the three crystal materials prepared, the medium carbon steel material with martensite is the most suitable for the acoustoelastic stress measurement.