Microscopic damage and macroscopic fragmentation are induced in rocks when they are impacted by water jets. A combination of macroscopic and microscopic methods was developed into an effective way of revealing the mechanism underlying rock breaking. Based on Computed Tomography (CT) and digital image processing, this paper proposes a quantitative approach to study the microscopic damage induced by water jets on coal. 3D reconstructions of induced damage filed were established by segmenting the greyscale slices. Relying on the established 3D reconstructions, the distributions of the induced damage in the horizontal and vertical directions were discussed. The results show that the distribution range of microscopic damage induced by pure water jets was significantly larger than that induced by abrasive jets due to different erosion mechanisms. Furthermore, the damage induced by both pure water jets and abrasive jets decreased as the punching depth increased, which resulted from the energy consumption caused by the resistance of the mixture composed of the initial arrival liquid and the coal debris. (C) 2018 Elsevier B.V. All rights reserved.