Abstract: To address the problem of underground coal mine gas drainage pipelines being easily blocked by coal slag,which significantly reduces drainage efficiency,this study proposes a self-propelled water jet dredging technology that operates without interrupting drainage. The coupled mechanism of jet penetration and impact crushing on coal slag was first revealed. Based on the law of conservation of momentum,the force balance equation of the self-propelled nozzle and the calculation model for the maximum propulsion distance were then established. Laboratory simulation tests systematically studied the effects of pump pressure,nozzle diameter,and front-to-rear nozzle number ratio on the self-propelled force and dredging length. The results show that the self-propelled force increases approximately linearly with an increase in each of the key parameters,reaching a maximum of 57 N. The dredging length increases with these parameters,but the growth rate slows down beyond a critical value, exhibiting a diminishing marginal effect. Through experimental optimization,a multi-hole directional nozzle structure with “ one front and four rear” orifices was determined,with a measured self-propelled force of 40 N and a maximum dredging length of 58 m. Field application in the Longfeng Coal Mine in Guizhou shows that the technology can completely remove coal slag and restore the effective flow cross-sectional area of the pipeline. After dredging,the gas mixture flow rate increased from 27. 56 m³ / min to 45. 61 m³ / min (a 65. 5% increase),the negative pressure loss at the terminal 20 m decreased from 10. 3 kPa to 6. 1 kPa (a 40. 8% decrease),and the negative pressure loss per unit length decreased from 93. 6% to 41. 2%. This technology can efficiently dredge blockages without interrupting the drainage process,ensuring the continued efficient operation of the gas drainage system.