Based on pressureless sintering technology, 6Al2O3-4Y2O3, 2MgO-2Al2O3-5SiO2, 3Al2O3-2SiO2 and B4C were used as sintering aids to prepare high density silicon carbide (α-SiC) with low content of sintering aids in this study. The phase, microstructure and mechanical properties of α-SiC prepared by different sintering aids and sintering process were analyzed. The results show that in terms of liquid phase sintering, adding 4.0% (mass fraction) 6Al2O3-4Y2O3 sintering aid, the α-SiC prepared by sintering at 1 850 ℃ has the best performance, and the density reaches 3.19 g·cm-3. However, at 1 300 ℃, the bending strength and fracture toughness of α-SiC prepared by this process decrease by 34.9% and 7.4%, respectively. In terms of solid phase sintering, the density of α-SiC prepared by adding 0.3% (mass fraction) B4C sintering aid at 2 000 ℃ reaches 3.14 g·cm-3, and it has excellent mechanical properties at room temperature and 1 300 ℃. The microstructure of α-SiC prepared by solid phase sintering and liquid phase sintering is compared and analyzed by DF-TEM. The mechanism of the evolution of bending strength and fracture toughness of α-SiC prepared by adding 6Al2O3-4Y2O3 and B4C sintering aids at room temperature and high temperature is preliminarily revealed.