Abstract: The process of filling aggregate to block hydrodynamic pathway has been explored in an empirical way for a long time. A numerical model (CFD-DEM) is established to study the mechanism of water closure. By simulating the settling velocity of aggregate particles in water, the starting velocity under different stacking thicknesses, the accumulation angle in natural state and hydrostatic water, the particle size partition effect in dynamic water and the pressure suppression capability of each particle group, the applicability of the model is verified. The carrying capacity of the flow is tested, and the flow field between the unconnected top area and the accumulation area corresponds to the upper limit of the starting velocity. When the carrying capacity of the flow field is much smaller than the aggregate-filling speed, it is easy to connect the top, and vice versa. The model considering water inrush channel, pressure, aggregate-filling speed, aggregate size, filling sequence, aggregate friction parameters and viscous flow of water is established to simulate the main stages of paving, filling and roofing of aggregate in hydrodynamic pathway, and the evolution process of velocity and pressure at different stages is obtained. A double-pathway closure model is established to simulate the two kinds of aggregate-filling schemes, and it is proved that giving priority to blocking one of the pathways is more reasonable. Finally, the processes of "early connection", "late superimposition" and "reverse growth" are summarized, and the effects of hydraulic gradient and carrying of flow capacity on accumulation length and number of boreholes are analyzed. The model for filling aggregate in hydrodynamic pathway provides a new research method for the process of closure.