Abstract: 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.