Abstract: In order to promote low-carbon development in the field of green mines and improve utilization efficiency of solid waste, a new type of high strength green cement based composite grouting material was obtained by employing silicate cement and fly ash as cementitious materials and using glass fiber powder (GFP) tailings for toughening. The effects of GFP dosage on the working properties, hydration products, setting time and mechanical strength of the composite grout were investigated through slurry property tests, mechanical strength tests, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermodynamic modeling. The mechanical bearing performance of the new grouting material cemented gravel was evaluated by the coal gangue aggregate grouting consolidation simulation test, revealing the grouting reinforcement mechanism of GFP modified fly ash-cement composite slurry on coal gangue. The results showed that addition of GFP helped to shorten initial setting time of fly ash-cement composite slurry, while the fluidity, water separation rate, and compressive strength of the stone body increased first and then decreased with the increase of dosage. When the content of GFP was 1%, the working performance of fly ash-cement composite slurry was the best. The initial setting time was shortened by 5.9%, and the compressive strength of 3 d and 28 d was increased by 12.6% and 37.8%. Microscopic characterizations confirmed that suitable GFP helped to improve the pozzolanic effect, promoting the consumption of Ca(OH)₂ to produce a large amount of hydrated calcium silicate products. The unhydrated GFP could exert a filling effect for improving the compactness of the matrix. The grouting reinforcement test showed that 1.0% GFP modified fly ash-cement grouting material effectively inhibited the growth of micro-cracks and pore structure of coal gangue cement during the load process, improving the multifractal characteristics. Its peak stress was increased by 12.1%, showing an enhanced mechanical bearing characteristic. The reinforcement mechanism could be attributed to the good synergistic coupling effect between cement, fly ash, and GFP. It would provide ideas for developing low-cost and high-performance green grouting materials in the deep coal mine engineering field.