<p>The composite structure formed by coupling backfill with rock exhibits a complex mechanical system. To investigate the mechanical properties and failure characteristics of tailings backfill rock composites, we designed and conducted uniaxial compression tests on tailings backfill phosphorite (TBR) composite specimens with different coupling dip angles, employing a 3D Full-field Deformation Measurement and Analysis System (XTDIC) and an Acoustic Emission (AE) system to monitor the failure process and uncover the failure mechanisms under uniaxial compression. The results of the study demonstrate that TBR coupling dip angles exerts a significant influence on mechanical properties. An increase in coupling dip angles leads to an elevation in peak stress and elastic modulus, accompanied by a reduction in peak strain. The most pronounced changes in mechanical properties occur between 45° and 60°. Concurrently, the primary load-bearing component transitions from tailings backfill to rock, thereby establishing a cooperative backfill rock load-bearing mechanism. Cumulative AE ringing counts effectively characterize crack evolution, and a Gaussian Mixture Model (GMM) based on AF-RA analysis was applied to classify crack types. The XTDIC measurements revealed the presence of localized high-strain zones that were developing along the interface under increasing load. Furthermore, an increase in coupling dip angles resulted in a shift in the failure mode from a tensile shear composite to a predominantly tensile mode. Based on the experimental analysis results, we constructed a uniaxial DEM model of the TBR composite to perform an in-depth analysis of its failure modes and crack evolution. This research provides essential references for stability analysis and control of TBR composite structures in backfill mining applications.</p>