<p>The ultra-low friction effect is easy to induce the sliding instability of deep coal rock, resulting in serious rockburst accidents. Using the self-developed ultra-low friction test device, the mechanical properties and precursor characteristics of deep coal seam sliding instability were analyzed from the perspective of ultra-low friction effect, and the effects of interface roughness (<i>JRC</i>), particle size (<i>D</i>), and filling thickness (<i>H</i>) on ultra-low friction-induced rockburst were revealed. The results show that: The main stage characteristics of the coal block slip instability process are “pre-slip-dynamic fracture-dynamic slip”. In the pre-slip stage, normal force and friction force decrease slightly, and the pre-slip accounts for about 31% of the total slip, indicating that the coal–rock system has entered an unstable stage. The dynamic fracture stage indicates the onset of structural failure. In the dynamic slip stage, the coal block is completely broken, and the normal force and the friction force decrease by about 84.5%. The fractured coal block slides out of the extrusion roadway at a high speed, and the dynamic slip accounts for about 69% of the total slip. An increase in <i>JRC</i> shortens the slip start time by 42.03%, whereas a decrease in <i>D</i> prolongs the slip start time by 54.35%, and an increase in <i>H</i> extends it by 53.33%. The functional relationship between coal–rock interface parameters, coal seam slip, and slip start-up time is established. The risk indicators are defined based on acoustic emission (AE) signal and slip displacement variation. By integrating the cross-intervals of these risk index, the sliding risk was classified into four levels: none, weak, moderate, and strong.</p>