To address the delayed strength development and uncertain rock-backfill interfacial stability of total-tailings paste backfill under low-temperature underground conditions, this study aims to quantify the coupled effects of slurry mass concentration, cement/tailing (C/T) ratio, curing temperature, and curing age on uniaxial compressive strength, and to clarify how interface roughness and curing age govern interfacial shear behavior and field strength. A silver–lead–zinc mine in Inner Mongolia was selected as the engineering background, and uniaxial compression, double-sided shear, SEM, and in situ strength tests were conducted. Results show that UCS increased with curing temperature, curing age, slurry mass concentration, and C/T ratio within the investigated ranges, with the comparative influence following the order: C/T ratio > curing age > curing temperature ≈ slurry mass concentration. With age, hydration products increased, pores and microcracks decreased, and structure densified. When joint roughness coefficient (JRC) increased from 0 to 26.76, cohesion rose from 93.31 to 965.57 kPa, and the failure mode shifted from interface slip to backfill shear. Increasing age from 3 to 7d raised cohesion from 611.02 to 965.57 kPa and the internal friction angle from 29.09° to 33.98°. Optimal conditions were 66% concentration and 15 °C, with C/T ratios of 1:4 (adhesive layer) and 1:8 (ordinary layer). Test results under various ratios and ages all indicate that the underground backfill has attained early self-standing and bearing capacity.