轨底月牙伤是一种常见伤损，但在检测过程中，B扫描数据在月牙伤的两侧时常出现37.5°回波信号，该类信号实际为幻象波，容易导致误判，增加误报率。根据幻象波的产生原理，基于60型钢轨的B扫描数据，对该幻象波进行了传播路径分析，通过声程计算与实际数据相比较，验证了分析的正确性。最后总结了该幻象波的特点，可为轨底月牙伤后续的检测识别提供理论支持。

Rail base crescent flaw is a common rail flaw, but there are some 37.5°echoes during detection sometimes, which actually are ghost echoes and they can easily lead to misjudgment and increase false positive rate. According to the generating principle of ghost echo, based on some B-scan data of 60 track, this paper analyzed propagation path, calculated spread distance and compared it to actual data, finally verified the correctness of the analysis. Furthermore, this paper summarized the characteristics of this ghost echo which can provide theoretical support for future detection and recognition.