根据超声波传播过程的仿真结果，提出波线-波面动态演化简化分析模型，以说明迟到波的形成机制及特性。分析认为，掠入射纵波是移动性头波的波源，以临界角传播的头波（横波）在相对侧的波型转换（转为纵波）后形成了迟到波；头波继续在相对侧反射形成了迟到波回波序列；由于主声束能量部分地逐渐转换为头波的能量积聚，造成了迟到波波幅可能大于底波波幅的现象。利用迟到波的一些特性，有益于更好地进行超声无损检测，波线-波面动态演化分析模型有助于一般超声检测问题的分析。

Based on the ultrasonic propagation process, this paper proposes a simplified analysis model of wave line-wave surface dynamic evolution in order to explain the formation mechanism and characteristics of the delayed wave echoes. The source of the moving head wave is the grazing incidence longitudinal wave, and a delayed wave echoes is generated from the head wave (transverse wave) at a critical angle due to the mode conversion (a head wave is transformed to a grazing longitudinal wave) at the lateral opposite surface of the specimen. The main beam energy is gradually transformed into the energy accumulation of the head wave, which results in the delayed wave echoes amplitude being larger than the bottom reflection amplitude. The ultrasonic nondestructive testing gets help with the head wave characteristics, the simplified analysis model of wave line-wave surface dynamic evolution contributes to the analysis of the general ultrasonic testing problems.