This work investigates the influence of calcium leaching on mechanical and physical properties of limestone powder (LS)–cement pastes cured under different temperatures. In order to achieve this goal, three different mass percentages of LS (10%, 30%, and 50%) were selected to replace cement, and the LS–cement pastes were cured under three different temperatures (5°C, 20°C, and 50°C). The LS–cement pastes were soaked in ${\mathrm{NH}}_4\mathrm{Cl}$ solution to accelerate the calcium leaching and simulate the leaching influence from water. The mechanical and physical properties including the compressive strength, flexural strength, Vickers hardness (VH), leaching depth, and electrochemical impendence spectroscopy (EIS) were conducted. The prediction model of VH and the relationship between equivalent VH and mechanical strength were built. The microstructure of LS–cement pastes is characterized by X-ray diffraction (XRD), thermogravimetric (TG), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests. Experimental results demonstrate that with the increase of LS, the decrease degree of mechanical and physical properties of LS–cement pastes increases gradually; Furthermore, the leaching damage degree of LS–cement pastes is the largest under curing temperature of 5°C, followed by 50°C and 20°C. The microstructure results reveal that the $\mathrm{Ca}{(\mathrm{OH})}_2$ in the leached zone of LS–cement pastes is completely dissolved, and the calcium leaching makes the LS–cement pastes cured under 5°C obtain the loosest structure and the most serious leaching damage, followed by 50°C and 20°C.