There are numerous connection interfaces between various components of an aero-engine. The fault acoustic emission (AE) signals collected by sensors are inevitably transmitted through the connection interfaces. The connection interfaces with different morphologies will inevitably have different effects on the propagation of AE signals. Causing differences between the received signal and the source signal. Therefore, it is necessary to study the effect of connection interfaces on the propagation of AE signals. This paper simulates the connection interfaces with different morphological features through finite element analysis. The concepts of relative contact area and relative height were proposed, and their effect on AE signal propagation was compared using waveform analysis, time-frequency analysis, and other methods. The effect of different morphological features on AE signal attenuation and diffraction were summarized. It is shown that the effect of relative contact area on AE signals is greater than that of relative height. Moreover, the smaller the relative contact area, the more obvious the diffraction phenomenon. The difference in the effect of different morphologies on AE signals is also greater. This paper elucidates the propagation characteristics of AE signals in the connection interface, reveals the effect of morphological characteristics, and provides guidance and reference for AE fault diagnosis.