Abstract: The size of V-cut angle has a non-negligible influence on the cracking of slabs in ancient rock mining. Taking the ancient cave complex of Qianlong Cave in Shepan Island,Sanmen County,Zhejiang Province as the research background and the rhyolitic crystalline glass chip fused tuff of the cave enclosure as the research object,this study combines fracture mechanics theory with indoor V-notch fracture tests. By varying the vertex angle β of the V-cut and the included angle α between the notch bisector and the horizontal direction,the crack initiation process of the tuff is analyzed. Additionally,the relationship between the crack initiation angle and the composite stress intensity factor in the crack initiation direction is deeply investigated,enabling the determination of the fracture mode of the crack surfaces. The results show that the optimal mining angle is achieved when the bisector of the Ⅴ-shaped incision forms an angle α=60°with the horizontal and the vertex angle β=20°. The ancient miners fully utilized the joint surface characteristics of the tuff,ensuring that the force required for slab separation was significantly lower than the rock's inherent strength. The rock failure mode was predominantly brittle fracturing,with minimal ductile deformation. This research holds great significance for the protection of intangible cultural heritage. It not only elucidates how ancient miners optimized stone quarrying techniques but also provides a scientific basis for optimizing modern stone extraction methods(e.g.,drilling and cracking techniques). Moreover,the findings offer valuable insights for understanding geological phenomena such as plane faults,joint systems,and seismic-induced rock fracturing in tuff. Ultimately,this study contributes to the rational preservation and interpretation of ancient quarrying practices in cultural heritage sites.