Abstract: For on-line inspection of the shell thickness of continuous casting billet,the ultrasonic shear wave reflection method is proposed.In this paper,the exciting and receiving process of electromagnetic ultrasonic shear wave transducer is simulated,the propagation of shear wave in continuous casting billet is analyzed,the reflected echo of the shear wave at the interface between the solid-liquid phases in the continuous casting billet is obtained.The Q460 billet shell of 10~50 mm thick is chosen as the test object.Through the finite element simulation software COMSOL,the variation curves of shear wave velocity with temperature at 800~1300℃ are obtained.According to the temperature distribution in the measured object,the average sound speed in the shell is obtained.Shell thickness is calculated by echo time and average sound velocity.The experimental results show that the above method can be used to measure the shell thickness of continuous casting billet.Corresponding to the time measurement error of 1~2 μs,the thickness measurement error is 2~5 mm.