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Influence of particle angularity on the suffusion in gap-graded granular soils remains unclear up to now. In this study, systematical numerical simulations that consider the particle shape as quasi-spherical polyhedra in different angularity are performed with the coupled discrete element method (DEM) and the computational fluid dynamics (CFD) approach. The suffusion of six gap-graded soil samples with 25% fines content is examined by imposing an upward seepage flow. Conventional triaxial tests are also conducted on the pre-eroded and post-eroded specimens to study the coupling influence of angularity and suffusion on the mechanical characteristics of granular soils. Fines loss, vertical displacement, soil strength, volume flow rate, microstructural analyses of force networks, the cumulative percentage of contact force, and the anisotropy of contact are investigated. Results turn out that the angularity intensifies the internal erosion resistance as the fines loss decreases significantly with the increasing angularity. The soil peak strength and friction angle are approximately linearly correlated with angularity. Erosion-induced particle redistribution reduces the degree of anisotropy of contact normal and contact normal force. This study may improve our understanding of the effect of particle angularity on suffusion with both microscopic and macroscopic evidence. [ABSTRACT FROM AUTHOR]