Abstract: With the gradual depletion of shallow metal mineral resources, deep mining has become an inevitable choice to ensure national resource security. However, the delamination failure of cemented fill roofs seriously affects operational safety in downward drift mining of deep metal mines. Although existing studies have explored backfill stability through theoretical analysis, similarity tests, and numerical simulations, there remains a lack of systematic research on the manifestation patterns, mechanical mechanisms, and prevention strategies of fill delamination under deep mining conditions. This paper investigates the delamination failure mechanism in downward drift mining at Maoping Lead-Zinc Mine through field surveys, statistical analysis, and refined numerical modeling. The research reveals the typical characteristics and spatial distribution patterns of fill delamination, clarifies its mechanical mechanisms, and proposes targeted control measures. Key findings include: ① delamination failure manifests as non-dynamic plate-like detachment, with initial failure occurring along reinforcement layers, featuring neat fractures and transverse crack propagation. Spatially, failures predominantly concentrate in narrow, deep sections of the ore body, while minimal damage occurs in thick ore zones, with lower failure probabilities in initial mining layers. ② Numerical simulations show that narrow ore zones with thinner fills fail to block stress transfer from surrounding rocks, resulting in maximum principal stresses exceeding UCS, whereas stresses in thick zones remain 2.0-4.0 MPa below failure thresholds. Subsequent mining induces transition from triaxial to biaxial stress states in upper fills, compounded by horizontal stress concentration from wall convergence, ultimately causing tensile splitting failures. ③ Based on failure mechanism analysis, a combined reinforcement scheme of “pre-embedded anchor bolts+welded mesh panels” is proposed. Field tests confirm that the optimized solution significantly suppresses delamination failure, with no detachment observed in exposed test stope roofs, validating its effectiveness. This study elucidates the mechanical essence of fill delamination in deep high-stress environments, providing valuable references for similar mining operations.