Abstract: In order to solve the problems of borehole wall collapse and well leakage in low-temperature drilling, a nano-composite cement slurry system suitable for low-temperature formations was designed. Combining the macroscopic test with microscopic analysis, the influence of nano-Al₂O₃ at low temperatures on the performance of silicate-sulphoaluminate composite cement slurry and the hydration process was studied. Based on the synergistic effect of hydration generated from the composite of ordinary silicate cement and sulphoaluminate cement, a nano-composite cement (NAC) was developed in conjunction with the nano-Al₂O₃, antifreeze agent EG, water reducing agent JS-1, and hardening accelerating agent TEOA. In addition, the low-temperature hydration process of NAC and its mechanism were studied through a combination of the scanning electron microscope (SEM), X-ray diffraction (XRD), and exothermic experiments of hydration. Experimental results showed that the nano-composite cement slurry had good initial fluidity at −9 ℃ with a pumpable period of 57 min, a 24-hour compressive strength of 6.9 MPa, and an initial and final setting time of 84 min and 101 min, respectively. The results of the study indicated that NAC had the right-angle thickening effect and superior performance at low temperatures, capable of meeting the requirements of borehole wall protection and loss circulation control in low-temperature formations.