The high-pressure grouting model of sandy soil particles was established by using the software PFC2D5.0 of discrete element numerical simulation. The occurrence and development law of wedge crack under different grouting pressure and grouting duration were compared. According to the change curve of porosity and pore pressure, the permeability, compaction and splitting in the process of high-pressure grouting are analyzed. Based on the results of core test in the field of seepage control and reinforcement of a dam, the composition and grouting mechanism of the consolidation body of the high-pressure rotary jet grouting without backflow are analyzed. The result show that the crack extension length and crack width are positively related to grouting pressure and grouting duration in a certain range. In the stage of drilling and grouting, the main function of grouting is infiltration and compaction. In the high-pressure jet grouting stage, the soil is broken into piles by using the high-pressure jet flow cutting mixing, high-pressure wedge splitting and high-pressure compaction to form a composite consolidation body.