Abstract: To study the effect of various loading rates and aggregate particle size gradations on the mechanical properties and fracture characteristics of cemented waste rock backfill, cemented waste rock backfills with various aggregate particle size gradations were conducted by uniaxial compression tests to analyze the mechanical properties with various loading rates, and the development and evolution of cracks inside the cemented waste rock backfill were studied with the help of acoustic emission system. The results show that the uniaxial compressive strength and elastic modulus of cemented waste rock backfill increased linearly with the increase of loading rate; with the increase of aggregate grading index, the uniaxial compressive strength and elastic modulus of cemented waste rock backfills display a rule of growth before decreasing; the damage mode of the specimen gradually changed from tensile damage to shear damage with the increase of aggregate grading index and loading rate, and the damage degree increased and the integrity decreased; the internal cracking of the specimen gradually changed from tensile damage to shear damage, and the damage degree increased. The development of cracks in the specimen is divided into four stages: compression-density stage, elastic deformation stage, stable crack expansion stage and unstable crack expansion stage.