In view of the deficiency of traditional bolt axial stress measurement and the defect of piezoelectric ultrasonic in nondestructive testing

a method of measuring bolt axial stress by using electromagnetic ultrasonic transducer（EMAT）is proposed.Transverse wave is generated in bolt skin layer by EMAT

and longitudinal wave is generated due to the reflection of wave transformation on bolt end face.The ray paths of longitudinal wave and transverse wave are analyzed

and the relationship of ratio between bolt axial stress and the time-of-flight of two modal waves is obtained.The experimental results show that the method can successfully receive the mode converted P-wave

and the sound velocity ratio of S-wave and mode converted P-wave has a linear relationship with the axial force of the bolt

so as to measure the axial force of the bolt.