Abstract: Under the circumstance of the skyrocketing energy cost, being the most efficient transportation method, railroad becomes the first choice for transferring people and commodities. At the same time, the increase of the train frequency and the running speed means more loads on the railroad and thus causes the growth of the fatigue crack of the railroad at more rapid rate. So the railroad has to be inspected periodically. Wheel probe is widely used in mid to high speed ultrasonic rail flaw detection equipment. In wheel probe, the incident angle is fixed. The wear of the rail of gauge side can cause the change of the refraction angle and thus affect the inspection results. The paper analyzed how the gauge side wear affected the inspection results, and tried to show how different level of gauge side wear changed the refraction angle. It was found that the gauge side wear could also cause the divergence of the beam. When gauge side wear was very severe, full reflection could occur. The simulation analysis presented in this paper can be used as the theoretical basis for design of effective and reliable wheel probe, thus improve the rail flaw detection capability.