When spontaneous combustion coal gangue is utilized as an aggregate in concrete, its physical properties are often inferior to those of natural gravel. To enhance its resource utilization in building materials, it can be reinforced with cement slurries. The effects of slurry wrapping reinforcement (water-cement ratio is 0.5~1.0) and composite reinforcement (water glass soaking, silica fume doping, pressure soaking) on the apparent density, water absorption, crushing value, needle-shaped flake content and particle size distribution of spontaneous combustion coal gangue aggregate were investigated. The changes in compressive strength and splitting tensile strength of concrete cube with each strengthening method were analyzed. Changes in shape parameters such as axle length ratio, roundness, and perimeter angularity coefficient after aggregate strengthening and their influence on concrete strength were summarized. Fractal geometry was introduced to verify the enhancement effect of aggregate shape on concrete strength through the fractal dimension of cracks at the time of specimen destruction. The test results show that: when the water-cement ratio is 0.7, the performance of the aggregate strengthened by coating is the best, and the 28 d compressive strength of concrete increases by 11.08%. The aggregate can be further strengthened by three methods (water glass immersion, silica fume doping, and pressure immersion) in composite slurry strengthening, and the 28 d compressive strength of concrete increases by 25.76%, 22.44% and 25.21%, respectively. The shape parameters of aggregate and the fractal dimension of cracks when concrete fails can quantitatively reflect the enhancement of concrete strength by aggregate strengthening.