<p>Subaqueous gravity flows can cause significant damage in geotechnical engineering, threatening both life and infrastructure. Although real subaqueous gravity flows are complex and may contain both particles and slurry, the consideration of the complicated compositions and their interactions are challenging. Here, a subaqueous gravity flow is explicitly considered as a particle-slurry mixture in water, modeled with coupled computational fluid dynamics (CFD) and discrete element (DEM). Both intra-phase and inter-phase interactions, including particle-particle, particle-slurry, particle-water, slurry-water interactions, are realized in the unified CFD-DEM framework. Particularly, the CFD model of subaqueous slurry as a Herschel-Bulkley (HB) fluid and the CFD-DEM model of a fluid-particle flow are respectively calibrated and verified. The collapses of five particle-slurry mixtures under water were then simulated, along with a reference case that a particle column collapses in water. The results show that, the occurrence of slurry can either promote or inhibit the particle motion, depending on the combined effect of fluid viscosity and density. The reduced potential energy shortly after the collapse seldom transfers to the kinetic energy of the flow in cases with slurry, in contrast to the efficient energy transfer in the reference case. A consistent trend is obtained between the runout distance and a proposed dimensionless number defined by energy transfer and time scale of the collapse. Interestingly, a strong correlation is captured between the positive relative particle-fluid velocity along the horizontal direction and the positive force along the vertical direction, indicating the promoted particle motion is due to the vertical interaction force.</p>