This paper uses experiments and simulations to investigate the fragmentation process of coal subjected to water jets. The experiments are conducted using computed tomography (CT) and digital image processing technology to reconstruct the damage field of an impacted coal core, and a numerical model is established based on the arbitrary Lagrange Euler (ALE) algorithm under the same impact condition. By analyzing the variations of the mechanical parameters in the simulation, this study reveals the element fragmentation mechanism. The results show that the fragmentation of an element can be divided into three stages. In addition, this research explains the formation and development of the punching based on the strain states in the simulation and verifies the deductions using experiment results. Furthermore, the paper also arrives at certain conclusions regarding variations of the damage field with coordinates. In the vertical direction, due to the resistance of reflux and the friction between jets and the punching wall, the kinetic energy of water jets is consumed gradually. Accordingly, both the distribution range and the degree of damage decrease with increasing standard depth. In the horizontal direction, the distribution of microscopic damage is characterized by locality, which occurs because of the attenuation of the acting effective stress.