Abstract: Grout-conserving bags. To characterize the local and overall development processes of the rapid interception more subtly and vividly, this study built a CFD-DEM fluid-solid coupling mathematical model of the roadway inlet under the given water head boundary according to the principle of a constant velocity. Then, given constant velocities of water inrush volumes of 2000 m³/h and 20000 m³/h, this study numerically simulated the construction process of water-blocking bodies by pouring and stacking aggregates with a grain size of 22 mm under the operating conditions with or without grout-conserving bags. The results show that: (1) Under both operating conditions, aggregates can accumulate to the roadway roof in the case of the low flow velocity but can accumulate only to 3/4 of the roadway height in the case of the high flow velocity. The main differences were that when grout-conserving bags were applied, water-blocking bodies were constructed to the same height in a shorter time while exhibiting higher blocking and lower water permeability; (2) In the case of the high flow velocity, aggregates still cannot accumulate to the roadway roof locally by simply increasing the grain size of aggregates but can swiftly accumulate to the roadway roof locally by simply increasing the pouring speed of aggregates; (3) As shown by the analytical results of the reasons for the differences mentioned above, there are two mechanisms of the rapid interception under flowing water by the borehole-controlled grouting with grout-conserving bags. One is that the bags themselves quickly formed part of the water-blocking body space. In other words, aggregates were put at the roadway bottom and filled in the roadway locally in advance. The other mechanism is that the high resistance and low permeability of the water-blocking bodies can reduce the reconstruction number of water-blocking bodies after being broken through in the later water-blocking stage as a result of the rapid pressure rise in the water-blocking section. Furthermore, these water-blocking performances of water-blocking bodies are conducive to the rapid coagulation of grout in the supplementary grouting stage.