An oblique incident longitudinal wave probe is used to form creeping waves on the inner wall of the tube to achieve the purpose of detecting defects on the inner wall of the thick-walled tube. First, the finite element method is used to simulate the creeping wave formation process on the inner wall of the obliquely incident longitudinal wave. Then, the laser ultrasonic visualization technology is used to observe the creeping wave formation process on the inner wall to verify the results of the finite element simulation. Finally, the developed ultrasonic flaw detector is connected the creeping wave probe obtains the reflected signal of the creeping wave on the artificial defect on the inner wall. The experimental results show that the ultrasonic longitudinal wave undergoes modal conversion on the inner wall of the tube to form a creeping wave. The creeping wave energy is related to the incident angle of the longitudinal wave, The distance between the probe and the defect affects the amplitude and time of the defect reflection signal. Longitudinal waves are only partially converted into creeping waves on the inner wall and there are other modes of ultrasound. The trial-produced creeping wave probe can effectively detect the inner wall defects of thick-walled pipes and provide an effective non-destructive testing method to ensure the safe operation of thick-walled pipes.