To explore the roles of the synergistic effects of CO₂ curing and nano-TiO₂ (NT) on the mechanical properties of low-heat portland cement(LHPC), the flexural and compressive strengths of LHPC were tested during various CO₂ curing times and NT dosages. The influence mechanisms were analyzed using testing methods such as scanning electron microscopy and thermogravimetric analysis. The results indicate that there is an optimal range for both NT dosage and CO₂ curing time when only considering the addition of NT or CO₂ for curing. Under the synergistic effect of CO₂ curing and NT curing, the compressive strength and flexural strength of LHPC pastes at 14 d and 28 d ages increased significantly when the NT content was 1% ~ 1.5% and 1.5% ~ 2%, respectively, within 24 h of CO₂ curing. This is due to the increase in the mass of calcium silicate hydrated gel(C-S-H), ettringite(AFt) and CaCO₃ in the samples. The fibrous C-S-H with a small aspect ratio refined the pore size of more than 50 nm. When CO₂ curing exceeds 24 hours and NT content is greater than 2%, the number of pores in the sample increases, and the generation of whisker like aragonite with larger aspect ratios and micro cracks reduces the mechanical properties. Considering the comprehensive mechanical strength and economy, it is recommended that the CO₂ curing time be 12 hours and the NT dosage be 1%. The research results provide a certain reference basis for improving the early mechanical properties of LHPC.