Abstract: In order to study the rock fracture and fissure propagation and evolution rule and to predict fissure (crack) length in the process of dynamic load intruding the rock, a mathematical model for describing relationship between the maximum impact force and the impact velocity during rock breaking was developed according to the Newton’s second law and the wave theory. Based on the relationship between static load and crack length of rock, the theoretical model of fissure length under impact load was established. In addition, researchers used a discrete element numerical simulation method to investigate the characteristics of fissure formation and propagation and the influence of impact velocity on crack length. The results indicate that tensile fissures are mainly formed under the impact force,and the radial cracks extend to rock free face, lateral fissures initiate from the damaged area and then extend to the inside of rock. Radial and lateral fissure lengths have a power function relationship with the impact velocity, and the numerical simulation results are consistent with the results of theoretical model. As the impact velocity increases from 15 m/s to 35 m/s, the rock breaking range and depth increase gradually, the radial crack length increased from 3.47 mm to 9.03 mm and lateral crack length increased from 7.29 mm to 14.58 mm. The research results can provide a theoretical reference for investigating rock fractures and fissure propagation under dynamic load intrusion and dynamic crushing mechanism.