Abstract: Investigation techniques, such as uniaxial compression tests, acoustic emission, digital image correlation monitoring, and scanning electron microscopy, were used from macroscopic and microscopic perspectives to investigate the effects of gangue particle-size gradation on the damage characteristics of cemented backfill. The peak strength, acoustic emission characteristics, and failure modes of cemented backfills with different gangue size gradations were examined. Test results indicated that with an increase in the gradation coefficient, the compressive strength of the gangue-cemented backfill first increased and then decreased. When the gradation coefficient is 0.5, the maximum compressive strength of the backfill is 4.28 MPa. The acoustic emission counts during the loading of gangue-cemented fills with different gradation coefficients passed through three phases: rising, active, and significantly active. The number of internal pores and cracks, as well as the uneven distribution of their locations, cause differences in acoustic emission characteristics at the same stage and variations in the strength of the backfill due to the different gangue particle-size gradations in the filler sample.