This study proposed a novel hybrid resolved framework coupling computational fluid dynamics (CFD) with discrete element method (DEM) to investigate internal erosion in gap-graded soils. In this framework, a fictitious domain (FD) method for clump was developed to solve the fluid flow around realistic-shaped coarse particles, while a semi-resolved method based on a Gaussian-weighted function was adopted to describe the interactions between fine particles and fluid. Firstly, the accuracy of the proposed CFD-DEM was rigorously validated through simulations of flow past a fixed sphere and single ellipsoid particle settling, compared with experimental results. Subsequently, the samples of gap-graded soil considering realistic shape of coarse particles were established, using spherical harmonic (SH) analysis and clump method. Finally, the hybrid resolved CFD-DEM model was applied to simulate internal erosion in gap-graded soils. Detailed numerical analyses concentrated on macro- -micro mechanics during internal erosion, including the critical hydraulic gradient, structure deformation, as well as particle migration, pore flow, and fabric evolution. The findings from this study provide novel insights into the multi-scale mechanisms underlying the internal erosion in gap-graded soils.