Abstract: Repairing borehole by self-propelled water jet drill bits is an efficient repair technique for downhole failed boreholes, and improving the borehole repair efficiency of self-propelled drill bits is crucial for enhancing the efficiency of coal mine safety production. The borehole repair efficiency of self-propelled drill bits is influenced by both drilling efficiency and coal particles transport efficiency in the borehole, which are mutually constrained. To achieve the optimal borehole repair efficiency, that is to maximize drilling efficiency while ensuring basic coal particles transport ability, CFD-DEM coupling was used to study the borehole repair process under different parameters. The transport patterns of coal particles under different annular ratios, jet pressures, coal particles sizes, and borehole angles were determined. The author established a theoretical model for the critical mass flow rate of coal debris transport under different annular ratios. The selection range of annular ratios under different jet pressures, coal particles sizes, and borehole angles was studied. The experiments on the transport patterns of coal particles in the annular space were carried out, and the experimental results are consistent with the numerical simulation results. The following main conclusions were obtained: the annular ratio, jet pressure, coal particles size, and borehole angle all affect the transport of coal particles in the annular space, with the annular ratio being the primary influencing factor. The flow velocity in the annular flow field and the pressure drop of the liquid-solid two-phase flow are the key parameters that determine the coal particles transport ability in the annular space. As the annular ratio increases, the flow velocity in the flow field first increases and then decreases, while the pressure drop of the liquid-solid two-phase flow decreases, resulting in the coal particles transport ability first improving and then declining. The transport capacity of coal particles is positively correlated with jet pressure, and negatively correlated with coal particles size and downward slant borehole angle. The optimal borehole repair efficiency parameters under different conditions were determined as follows: when the jet pressure is 0−10 MPa, an annular ratio of 0.53 is selected; when the jet pressure is 10−15 MPa, an annular ratio of 0.44 is selected; when the jet pressure is greater than 15 MPa, an annular ratio of 0.39−0.44 is selected. When the coal particles size is 0.5−3.0 mm, an annular ratio of 0.53−0.60 is selected; when the borehole angle is −60°−0°, an annular ratio of 0.44 is selected. The optimal borehole repair efficiency parameters provide a basis for the selection of drill bits and pipe diameter parameters under different conditions during downhole borehole repair.