Abstract: To investigate how deformation localization develops in sandstone during failure under acidification, we conducted triaxial compression tests on sandstone samples exposed to acidic chemical corrosion. The experiments used a visual servo-controlled triaxial compression system and employed three-dimensional digital image correlation (3D-DIC) technology to analyze spatiotemporal patterns of deformation. The results revealed several key findings: (1)Under triaxial compression, deformation localization in sandstone develops progressively, with strain values gradually concentrating along the main fracture surface, particularly at the initial 5% strain points. (2)At a constant confining pressure, the width of the deformation localization band on the sandstone surface first increases and then decreases as immersion time in acid solution increases. (3)Using 3D-DIC, we obtained detailed surface deformation data in three dimensions. Analysis of the spatial and temporal evolution of the largest 5% strain points during loading showed that the angle between the deformation localization zone and the specimen's axial direction decreases as immersion time increases. Additionally, with longer immersion, the fracture surface evolves from a surface feature to a planar one.