Abstract: In order to study the law of crack initiation and propagation of mode I crack in rock under blasting and the related dynamic fracture parameters during the propagation process, the SREN (Semicircle and rectangle with edge notches) specimens made of sand-stone with pre-crack and detonators were used for explosion experiments.In the experiment, three different lengths of pre-crack and crack propagation gauge (CPG) velocity measurement system were used to obtain crack initiation and propagation time, and the propagation velocity was obtained and corrected by fractal theory.This paper also used the AUTODYN code to carry out numerical simulation.Considering that rock was a typical brittle material and the fracture area near the crack tip was small deformation, the rock material adopted linear equation of state, elastic strength criterion, principal stress failure model and the JWL equation of state is used for the explosive material to describe the relationship between pressure and density during the explosion process.The simulation results can be used to observe the crack propagation path and verify the rationality of the new specimen.Using the displacement extrapolation method, the stress intensity factor of crack initiation and propagation was calculated by finite element software ABAQUS.Combined with the fracture time measured by CPG, the dynamic fracture toughness of each specimen under different extension lengths was obtained.By using the above experiment combined with numerical simulation, the results show that the large-sized SREN specimen used in this paper can be less affected by the reflected tensile stress wave, and applied to the measurement of dynamic fracture parameters of brittle materials.With the increase of the pre-crack length, the crack initiation time becomes longer, the propagation average velocity becomes smaller and the fluctuation becomes more stable.The increase of the pre-crack length will also lead to the decrease of crack initiation toughness.The propagation toughness is not fixed and will be greater than the cracking toughness and gradually decrease.