<p>The presence of fractures in rock masses significantly impacts engineering safety, making it crucial to elucidate the failure mechanisms of fractured rock and investigate fracture initiation and propagation under various loading conditions. In this study, for the first time, in-situ four-dimensional computed tomography (4D-CT) imaging and digital volume correlation (DVC) techniques were employed to comprehensively investigate the failure mechanisms of fractured mudstone under triaxial conditions. Through real-time 4D-CT visualization, the complete deformation process of mudstone specimens with pre-crack at 0°, 45°, and 90° orientations was captured. The results reveal distinct initiation patterns: mid- crack nucleation in 0° and 90° specimens versus tip-initiated cracking in 45° specimens. Notably, post-peak macroscopic crack propagation in 0° specimens deviated from the initial fracture path, exhibiting wing crack development at crack tips. DVC analysis quantitatively characterized the displacement and strain field evolution during the deformation and failure process of fractured mudstone, unveiling its three-dimensional deformation localization patterns. Finally, based on the in-situ 4D-CT triaxial loading experiments and structural surface stress characteristics, this study provides an in-depth discussion on the fracture initiation and propagation mechanisms of single-fractured rock under triaxial compression. These findings substantially advance the theoretical understanding of fracture initiation-propagation mechanisms in fractured rock masses.</p>