Abstract: In the process of water inrush and roadway blocking in coal mine, the mechanism of aggregate connecting roof and dam break has been lack of intuitive and effective research means. Through the establishment two-phase flow coupling calculation model by CFD-EDEM, single hole continuous grouting test was carried out under the conditions of static water and dynamic water respectively, which verified that the fine aggregate is more suitable for the process of transportation and bedding. The results show that when the flow rate is small, there will be a large number of unfilled areas between the boreholes. Under the condition of large flow rate, the top area will grow upstream against the trend, and finally the whole section will be connected. The concept of particle arch is introduced to analyze the mechanical mechanism of aggregate random connection, and the shear instability model of skeleton is proposed. The seepage instability mechanism of accumulation body and the migration form of aggregate in the process of dam break are explained by the concept of piping. Combined with the engineering data, the difference between the static water closure and the dynamic water closure in the project investment and construction difficulty is verified. It is pointed out that the dynamic water closure needs to go through many times of dam failure and repeated perfusion before the final closure is successful.