Abstract: Coalbed methane (CBM) development is of critical importance for alleviating the shortage of natural gas in China. The construction of a large-scale fracture network during acid-based volumetric fracturing is key to achieving efficient CBM extraction. An experimental investigation of the anisotropy of fracture toughness and strain localization in anthracite subjected to acid-based fracturing fluid is essential for a deeper understanding of crack initiation and propagation during reservoir fracturing. To this end, three-point bending tests were conducted on straight-notched semi-circular bending (NSCB) specimens of Qinshui anthracite with five different bedding plane angles (0°, 22.5°, 45.0°, 67.5°, and 90.0°) after treatment with pressurized water-based and acid-based fracturing fluids. The anisotropic characteristics of fracture toughness of coal specimens treated with acid-based fracturing fluid were examined. Using digital image correlation method (DICM), the anisotropic evolution of the strain localization zone (SLZ) and the high-strain zone (HSZ) was explored at different loading stages, and a power-law relationship between them was established. Meanwhile, through monitoring of the crack opening displacement (COD) at various loading stages, the dynamic response of crack opening displacement as a function of load evolution was quantitatively characterized. The three-dimensional structural reconstruction of coal specimen fracture surfaces was carried out using Geomagic three-dimensional inspection software and Surfer three-dimensional mapping software, enabling fine meshing and three-dimensional contour mapping to explore the anisotropic characteristics of fracture surface roughness. The results indicate that, compared with the water-based fracturing fluid group, the acid-based fracturing fluid group exhibits a more pronounced reduction in fracture toughness with increasing bedding angle, suggesting a decreased resistance to crack propagation. Among the five bedding angle groups, the length of the strain localization zone in coal specimens treated with acid-based fracturing fluid showed an increasing trend relative to that in the water-based group, with the most significant difference observed at a bedding angle of 45.0°, where the length increased by 36.184%. The smallest difference was observed at 90.0°, with an increase of only 1.913%. Under the action of the two types of fracturing fluids, different power-law relationships were followed between the lengths of the strain localization zone and the high-strain zone. In addition, a mathematical model describing the variation of crack opening displacement with different measurement line heights on the coal specimen surface was established. The relevant findings provide an experimental basis for the study of crack initiation and propagation mechanisms in acid-fractured anthracite and offer theoretical references for the design of acid-based coal reservoir fracturing, the formation mechanism of complex fracture networks, and their control methods.