<p>Layered rock masses are widely distributed in underground engineering. The dynamic loading induced by drilling and blasting during tunnel excavation often triggers shear-dominated fractures along bedding-controlled weak planes. Consequently, the dynamic Mode II fracture toughness of orthotropic rocks becomes a key parameter governing crack initiation, propagation, and the potential instability of the surrounding rock mass. However, the influence of bedding plane orientation on the dynamic Mode II fracture toughness and fracture mechanisms remains insufficiently understood. In this study, a shear-box test is proposed to determine the dynamic Mode II fracture toughness of orthotropic rock with different bedding plane (0°, 30°, 45°, 60°, 90°), and a modified fracture type criterion is established to predict fracture mechanism and initiation angle. Results show that Mode II fracture is successfully achieved in orthotropic phyllite specimens under various bedding angles and loading rates, and the dynamic Mode II fracture toughness increases with increasing loading rate and bedding angles. However, the anisotropy index (fracture toughness ratio of vertical plane at <i>β</i> = 90° to bedding plane at <i>β</i> = 0°) decreases with the increase of loading rate and approaches 1 under extreme high loading rate. This study provides new theoretical insights and experimental evidence for understanding the dynamic fracture behavior of layered rock masses.</p>