Abstract: To address the problem of frequent coordination imbalance among coal slag generation, migration, and annular bearing during hydraulic annular cutting in in-seam boreholes, models for slag particle size and generation rate during slotting were established and experimentally verified. The characteristics of slag particle size, generation rate, migration behavior, and annular bearing capacity were clarified. Borehole blockage criteria based on the migration velocity ratio and bearing load ratio were proposed, and the influence of jet pressure, drill pipe rotation speed, and nozzle diameter on the coordinated slag discharge state was revealed. Axially from the slotting position, the borehole can be divided into three consecutive zones: a suspension zone, a deposition zone, and an accumulation zone. Slag settlement in the deposition and accumulation zones significantly reduces the water flow transport capacity and the annular bearing capacity for coal slag. Compared with jet pressure, increasing the nozzle diameter beyond the threshold of 2.5 mm is more likely to cause the bearing load ratio to exceed the borehole blockage threshold, leading to annular overload with excessive slag and subsequent borehole blockage. Increasing the drill pipe rotation speed can reduce both the migration velocity ratio and the bearing load ratio below the blockage threshold, thereby enhancing water flow transport and annular bearing capacity and promoting slag discharge. Based on these findings, a coordinated slag discharge map involving jet pressure, drill pipe rotation speed, and nozzle diameter was established, providing a theoretical basis for the synergistic optimization of coal breaking efficiency and safe slag discharge in hydraulic annular cutting.