Abstract: In order to study the fracture factors in the rock mass under the blasting load, the dynamic finite element software ANSYS/LS-DYNA was employed to study the fracture mechanism of the rock under blasting load,and the influence of initial stress,free boundary and joint on rock dynamic fracture was discussed. The results indicate that the radius of the crack zone under the combined action of the explosion gas and the stress wave is1.85 times as the stress wave alone, and the existence of the explosive gas makes the rock breaking process more effective; when the lateral pressure coefficient maintains constant, the increase in the initial stress causes the decrease in the crack radius; The reflected tensile stress wave from free surface leads to crack initiation parallel to the free surface; The free surfaces parallel or perpendicular to the joint has great influence on the distribution of blasting crack. The research results can provide reference for blasting excavation engineering medium hard rock.