Abstract: In this paper, the ultrasonic propagation characteristics of Al₂O₃/EP composites are simulated by COMSOL Multiphysics software. For particle reinforced resin matrix composites, it is difficult to detect due to the high sound attenuation characteristics of the resin matrix and the existence of heterogeneous particles and multi-connection interface properties. In this paper, a numerical simulation model is established for the typical particle agglomeration phenomenon in the microstructure of Al₂O₃/EP composites for GIS and the gap characteristics at the particle/resin interface. The effects of different Al₂O₃ particle shapes and contents on ultrasonic propagation and the effects of different interface gap sizes on ultrasonic energy penetration were compared. The results show that the geometric shape and agglomeration of Al₂O₃ particles have a certain influence on the propagation of ultrasonic wave, and the polygonal agglomerated particles have a greater attenuation effect on ultrasonic wave than the circular particles of the same size, about 1.9% higher; With the increase of the content of Al₂O₃ particles, the acoustic wave propagation speed slows down due to the increase of the heterogeneous connection interface. Compared with the 10% primary bottom wave pressure signal, the 20% content is enhanced by about 40%. The research on the influence of the gap size on the interface between the particles and the matrix shows that the ultrasonic energy penetrating the Al₂O₃ particles is greatly weakened with the increase of the gap size. Comprehensive analysis, Al₂O₃ particle reinforced resin matrix composite GIS basin ultrasonic testing, the influence of ultrasonic attenuation characteristics from large to small in turn is the existence of Al₂O₃/EP interface gap— heterogeneous connection interface— particle geometry.