The shear mechanical behavior of cemented backfill under complex geothermal conditions is critically important for mine safety and stability. This study investigates the effect of curing temperature on the shear properties of backfill material composed of high-purity silica fume as aggregate and ordinary portland cement as binder. Direct shear tests were systematically conducted under varying curing temperatures (2°C, 20°C, 35°C and 50°C). Microstructural evolution was characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results indicate that the peak shear stress increases approximately linearly with rising temperature, with an enhancement ranging from 228% to 433%. Cohesion exhibits a nonlinear quadratic increase from 68 kPa at 2°C to 554 kPa at 50°C, whereas the internal friction angle increases only moderately from 38.66° to 45.29°. Microstructural analysis reveals that elevated temperature promotes the formation and development of C-S-H, which evolves from dispersed particles into a continuous network and eventually dense clusters. Coupled with pore-filling effects from ettringite and other hydrates, these changes significantly improve the compactness and cementation of the material. These findings provide a theoretical basis for the mechanical design and thermal adaptation of backfill in high-temperature deep mines and cold-region mining operations.