Abstract: To further reveal the influence mechanism of the size proportion of coal-rock assemblages on ultra-low friction rockbursts, a theoretical benchmark model of the ultra-low friction effect was established based on blocky rock masses. Starting from structural characteristics, the experimental model of blocky rock masses was linked with the “whiplash effect”. A sandstone-coal-sandstone block structure was adopted to simulate the actual roof-coal seam-floor conditions encountered in underground coal mining. Combining a self-developed ultra-low friction test device with FLAC^3D numerical simulation, the influence of the height-width ratio of the “working block” on the stability of the block structural system model under the same stress environment was analyzed. The horizontal displacement and horizontal acceleration of the “working block” were used as indicators to characterize the intensity of the ultra-low friction effect. The correlation between the susceptibility of generating the ultra-low friction effect in the system and the abrupt change characteristics of the horizontal displacement of the “working block” was analyzed. The results show that the size proportion of the “working block” has a significant influence on the triggering threshold of the ultra-low friction effect. As the height-width ratio of the “working block” increases within a certain range, its horizontal displacement exhibits a nonlinear response of first decreasing and then increasing, while the stability first increases and then decreases. Significant instability characteristics are observed in the typical case “h-100 mm” (i.e., the height of the “working block” is 100 mm, with a height-width ratio of 1:1): the x-direction acceleration time-history curve shows sustained asymmetric oscillation deviating from zero, producing persistent and irreversible effects; the z-direction acceleration is amplified in phase, triggering instability sliding induced by the ultra-low friction effect until severe slip instability of the system occurs.