The extraction of coal resources generates substantial quantities of coal gangue, which not only causes severe environmental pollution but also poses significant safety hazards due to its spontaneous combustion propensity. Utilizing this waste material is crucial for mitigating environmental impacts and reducing pressure on natural aggregate resources. 45 specimens were fabricated by controlling the water-cement ratio, compaction pressure, and gangue particle size, and uniaxial compression testing was subsequently conducted. Results demonstrate that compressive strength is predominantly governed by the water-cement ratio, while lesser sensitivity is exhibited to compaction pressure and gangue particle size. Specifically, compressive strength was found to increase significantly with higher water-cement ratios, to decrease with larger gangue particles, and to increase with greater compaction pressure. Scanning electron microscopy revealed that the water-cement ratio dictates the compactness of micro-cementation structures and interfacial bonding quality, increased ratios were observed to enhance cement hydration while reducing interfacial microcracks. Based on the uniaxial tests and scanning electron microscopy observations, a particle flow numerical model was established. The results indicate that with an increase in the water-cement ratio, the number of contact force chains at the specimen’s peak stress point increases, the contact force within the strong force chains increases, and the number of cracks correspondingly decreases. Failure modes were observed to transition progressively from tensile-dominated to mixed tensile-shear, and ultimately to shear failure as the water-cement ratio increased.