Abstract: Internal erosion due to migration of fine particles of gap-graded sand and gravel soil by seepage through void channels between coarse particles. This migration leads to the redistribution and deformation of the soil skeleton and thus threatening the safety and stability of earth and rock dams, embankments and other projects. Particle morphology and its correlation with other parameters is one of the most important influences on the occurrence of internal erosion in soil structures. In this study, a custom-developed soil internal erosion apparatus was employed to conduct tests on three types of gap-graded sand and gravel soils with varying particle morphologies under different hydraulic gradients. These tests aimed to elucidate the macroscopic evolution characteristics of soil internal erosion. Using the computational fluid dynamics-discrete element method (CFD-DEM) coupling approach, the combined effects of coarse particle morphology and fine particle content, with varying degrees of sphericity, on internal erosion were investigated from the perspectives of force chains, contact forces, and coordination numbers. The findings indicate that when the content of fine particles is the same, the higher the sphericity of coarse particles in the soil, the more significant is the number and magnitude of fine particles lost. The self-locking effect of non-spherical particles enhances the permeability resistance of gap-graded sand and gravel soils. Additionally, the sphericity of coarse particles of the soil is inversely related to the average coordination number. These results provide important basis for assessing the internal erosion risk of gap-graded sand and gravel soils.