The precision of fault feature extraction and damage locating by AE signal is determined by its propagation characteristics in different structures. In this paper, a two-dimensional explicit finite difference method is extended in AE signal model building of shaft, stepped shaft and stepped shaft with too withdraw groove; the constitutive behavior of the shafts under impact load is analyzed; the experiments of three different structural shafts are conducted. The results of the simulations and the experiments reveal that the propagation characteristics-reflection, transmission, attenuation-of AE signal in shaft, stepped shaft and stepped shaft with too withdraw groove are simulated correctly by using the model of AE signal built through the explicit finite difference method.