Abstract: Due to the narrow slagging space of drilling and the easy accumulation of coal particles, it is easy to cause the phenomena of jet hole, hole plugging and holding drill in the process of hydraulic slotting in drilling along coal seam, which seriously affects the success rate and safety of slotting construction in drilling along coal seam. In view of the above problems, the drilling shape of slotting drilling in drilling along coal seam was studied.By analyzing the phenomenon of drilling subsidence, the slotting drilling was divided into three stages: accelerated sinking section, inclined sinking section and opening section. The phenomenon of drilling plugging model and hole plugging in each stage were analyzed. The coal cinder movement in each stage of slotting drilling was studied. It is obtained that the coal cinder movement in the accelerated sinking section is dominated by water lift and drag force, the coal and water mixed two-phase fluid is fully mixed through the disturbance of drill rode rotation; in the inclined sinking section, the external spiral rotation power of the drill rode is the main driving force to drive the movement of coal cinder. Through a large number of field tests, the parameters of slotting pressure and drill rode speed under different coal seam conditions of firmness coefficient are obtained. It is concluded that with the increase of coal seam firmness coefficient, the optimal slotting pressure increases, but the reasonable drill rode speed decreases, the technology of slotting slag discharge in drilling along coal seam has been formed, which includes reasonable selection of slotting pressure and drill rode speed parameters, control of pressure adjustment gradient, observation of water and slag return at orifice, and extend the time of low-pressure hole washing after slotting. The field test shows that the technology of slotting slag discharge can effectively avoid the risk of slotting and hole plugging, ensure the safe implementation of slotting in drilling along coal seam, improve the success rate of slotting, greatly improve the effect of drilling gas drainage, and effectively promote the application of the technology of hydraulic slotting and antireflection and pressure relief in drilling along coal seam.