Abstract: Given the practical situation of a copper mine and using the means of combining laboratory experiments with numerical simulation，the characteristics of the mechanical strength cemented classifying tailings backfilled by new cementing agent and the stability of them used as stope roof are studied. Uniaxial compression test and Brazilian splitting test results show that in the curing age of 7 d, 14 d, 28 d and 60 d, the uniaxial compressive strength, and tensile strength of cemented classifying tailings backfilled by new cementing agent when mixture ratio are 1 to 6 and 1to 12 are higher than that of cemented classifying tailings backfilled by 42.5# cement when mixture ratios are 1 to 4 and 1 to 8.While the early compressive strength and tensile strength of the former is superior to the latter. The numerical simulation results of FLAC^3D show that the strength of cemented classifying tailings backfilled by new cementing agent can meet the requirements of filling stope roof.