Abstract: To address the issue of rockburst disasters induced by the fracture of thick-hard roof strata, focuses on deep extra-thick coal seams with thick-hard roofs. By integrating theoretical analysis, mechanical modeling, engineering experiments, and field monitoring, the fracture characteristics of thick-hard roofs under backfill mining conditions were investigated. A mechanical model for the settlement of thick-hard roofs based on thick plate theory was established, and the equation for the deflection curve of the thick-hard roof under mining-induced conditions was derived. The influence characteristics of the effective boundary size and filling rate of the filling body on the deformation of the roof were quantified, and the relationship between thick and hard roof and effective filling parameters was clarified. With the increase of filling rate, the settlement of the roof in the effective boundary area decreased significantly, the effective boundary size of the filling body increased accordingly, and the contact area of the roof increased. The settlement curve of thick and hard roof showed a downward trend as a whole. Based on this, a method for controlling the height of overburden failure was proposed using an equivalent mining height model. The spatial evolution characteristics of thick-hard roofs under backfill conditions were elucidated, and the disaster prevention and control mechanism of backfill mining in deep extra-thick coal seams with thick-hard roofs was revealed. Practical validation was conducted using a “dual synergy” backfill ratio enhancement technology. The results showed that after applying the “dual synergy” enhancement technology, the proportion of uncontacted roof areas in the total settlement of the thick-hard roof under four backfill ratios was 86%, 80%, 72%, and 55%, respectively. The effective boundary range expanded significantly, and the backfill ratio increased from 75% to 90%, while the effective backfill space grew from 2.63 m to 3.25 m. This increased the contact area between the backfill material and the thick-hard roof, enhancing the load-bearing capacity of the backfill by approximately 55%. The average energy and frequency of microseismic events decreased significantly. These findings demonstrate that the “dual synergy” backfill ratio enhancement technology achieved disaster prevention and control objectives in deep thick-hard roof working faces, significantly mitigating rockburst risks and ensuring the safe mining of extra-thick coal seams under deep thick-hard roof conditions.