###### Abstract  
In deep underground engineering applications, such as coal mining, coal-rock masses are frequently subjected to repeated loading and unloading conditions. Understanding the evolution mechanisms of their internal three-dimensional fracture fields has become a critical scientific challenge. This study utilized X-ray Microscopy (XRM) to observe changes in internal fractures of coal samples after each loading-unloading cycle, reconstructing the internal fractures and mineral particles. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) were employed to analyze the surface morphology and mineral composition of coal sample cross-sections. The experimental results revealed that: (1) With an increasing number of loading-unloading cycles, the samples' volumes initially decreased and then expanded, with the expansion accompanied by rapid propagation of CT-scale fractures; (2) During the linear elastic phase, micro-fractures developed progressively but remained small, while sustained stress caused these fractures to interconnect, eventually leading to macroscopic failure; (3) Hard mineral particles within the coal samples, such as iron ore, acted as barriers to crack propagation. These findings indicate that the evolution characteristics of the internal fracture fields in coal-rock masses are influenced by stress state, pre-existing fractures, and the distribution of mineral particles. c 2025 15 2556 2025 2556 20  
-fracture networks significantly alter coal seam permeability, which affects the migration of fluids such as gas and groundwater within the seams [7,8]. Therefore, investigating the three-dimensional morphology and propagation mechanisms of internal cracks in coal under cyclic loading is of critical importance for evaluating mining stability, preventing water-related hazards, and managing gas extraction and utilization. During the fracturing of rocks, various physical signals, including acoustic, electrical, magnetic, and thermal emissions, are generated. Researchers have extensively applied geophysical monitoring methods such as acoustic emission [9,10], surface potential [11,12], electromagnetic radiation [13,14,15], micro-current detection [16], and infrared radiation [17,18]. These methods are advantageous for their non-destructive and efficient monitoring capabilities, making them valuable tools for underground coal-rock mass observation and early-warning systems. However, since fracture formation is intrinsically linked to changes in the microstructure of the material, comprehensively understanding damage mechanisms and their microstructural characteristics requires microscopic-scale research. Although geophysical methods can dynamically monitor the evolution of fractures in coal-rock masses under load in real time, they are limited in their ability to spatially characterize microscopic fracture structures with high accuracy. Industrial micro-CT technology has emerged as a powerful tool for the precise characterization of internal cracks in coal-rock masses, offering non-destructive detection, high-resolution imaging, and three-dimensional visualization capabilities. This technology is widely employed in microscopic studies of oil and gas reservoirs as well as coal-rock damage. For example, [PERSON] et al. [19] constructed micro-meso-scale geometric models of coal using X-ray CT imaging and three-dimensional reconstruction techniques. [PERSON] et al. [20] conducted real-time CT scanning of thermally damaged granite under compressive loads, analyzing porosity and crack length to characterize microcrack behavior. They explored how loading influenced the three-dimensional distribution of microcrack volumes and the orientation-dependent length of two-dimensional cracks. Similarly, [PERSON] et al. [21] utilized real-time scanning to extract pores and fractures from reconstructed three-dimensional sandstone cores, investigating the size and distribution of the largest clusters. [PERSON] et al.