The low early strength and slow curing characteristics of natural hydraulic lime (NHL) limit its wide application in stone cultural relics. Improving its early comprehensive performance is a study with significant practical value. Triethanolamine (TEA) is a commonly used early-strengthening agent in cement, while diethyl carbonate (DEC) is a highly efficient and stable CO₂ absorber. In this paper, we combine the advantages of these two materials to compound-modify natural hydraulic lime slurry (NHL) to improve the efficiency of early hardening reactions and mechanical strength. The results show that the compounding modification of TEA and DEC exhibites an efficient synergistic effect, significantly promoting hydration and carbonation reactions. The total porosity within the slurry is reduced, contributing to a denser and more stable matrix structure. The optimal modification effect is achieved with TEA-DEC mass fraction of 0.3% and 0.5%.. The initial and final setting times are shortened by 18% and 45.5%, respectively. The mechanical properties are obviously improved, with compressive strength increased by 27.3% after 28 days of maintenance, reaching the strength level of NHL5 in the European standard.