The investigation on dynamic shear fracture behaviour of rocks subjected to the simulated geo-stress is of great importance for deep rock engineering. Four groups of dynamic mode II fracture tests with different axial pre-forces were conducted on the granite short core in compression (SCC) specimens using a coupled static–dynamic loading system. It can be found that dynamic mode II fracture toughness rises with increasing loading rate at a given pre-force ratio and decreases with increasing pre-force ratio at a given loading rate. Total fracture toughness exhibits evident rate dependence and it is almost independent of the pre-forces. An empirical model was established to describe the influence of the pre-force and loading rate on the Mode II fracture toughness. Deformation, damage and fracture characteristics of rock were elaborated based on surface deformation field. The results indicate that (1) The original damage caused by pre-force increases with the pre-force ratio; (2) The fracture path is independent of pre-force ratio and the loading rate in the studied range; (3) At a given pre-force ratio, the loading rate has a significant effect on the final failure pattern of the SCC specimen. In addition, a novel relative shear velocity (RSV), defined as the ratio of relative shear displacement and time spent from deformation onset to the generation of complete shear fracture, is proposed to depict the dynamic shear crack propagation. The results indicate that the RSV increases with loading rate irrespective of the pre-force, showing a power function relationship with loading rate. Highlights: Dynamic mode II fracture tests were conducted on the granite short core in compression specimens using a coupled static–dynamic loading system. The relationship between dynamic mode II fracture toughness with axial pre-force and loading rate is analysed qualitatively and quantitatively. Deformation, damage and fracture features of granite were elaborated using three-dimensional high-speed digital image correlation technique. A novel index, relative shear velocity, based on surface displacement field, is proposed to depict the dynamic shear crack propagation. [ABSTRACT FROM AUTHOR]