The geometrical structure and mechanical characteristics of backfill body are factors influencing the quality of filling material. In this study, similar simulation tests were conducted to investigate flow sedimentation law of filling slurry; uniaxial and triaxial compression tests on backfill body samples were carried out to reveal the structural characteristics and strength distribution law of backfill body, and to capture the deformation characteristics and failure mode of uneven backfill body samples under different confining pressures. The results show that: (1) Two boundaries and three areas of coarse aggregate, fine aggregate, cement-tailing exist in backfill body in stope. The strength of backfill body samples has an “S” distribution of diminution-enlargement-diminution along the flow direction of filling slurry. (2) Stress-strain curves of backfill body samples under triaxial compression are composed of five stages of the compaction, i.e. the elastic, the plastic, the post-yielding, the strain softening and the residual stress stages. The strength of backfill body samples in the same area increase with the increase of confining pressure. The strength of backfill body samples in different areas under the same confining pressure is in the order as cement-tailing area > fine aggregate area > coarse aggregate area. The cohesion of backfill body samples in different areas is in the order as cement-tailing area > fine aggregate area > coarse aggregate area, and the internal friction angle is in the order as coarse aggregate area > fine aggregate area > cement-tailing area. (3) The quantity of macro-failure cracks of backfill body samples is on the up-trends as the confining pressure increases, the main macro-failure modes are shear failure of single ramp, tension-shear failure, Y-shaped shear failure. The results can provide theoretical basis for the design of the amount and position of drill holes for filling, also provide theoretical basis for stability analysis of filling material.