γ-Al2O3 as an additive was adopted into nano silica porous thermal insulating material to reduce the volume shrinkage at higher temperatures.The effects of sintering temperature and mass ratio on volume shrinkage were investigated,and the effect of γ-Al2O3 on thermal insulating properties was also analyzed.The results show that the volume shrinkage strongly increases with temperature,and the additive of γ-Al2O3 can significantly reduce the volume shrinkage.When the mass ratio is 5%,the volume shrinkage decreases from 10.49% to 3.47% at 1 000℃.Moreover,better result can be achieved with increase of mass ratio.Meanwhile,γ-Al2O3 has little influence on thermal conductivity at higher temperatures.Finally,the mechanism of shrinkage restraint is illuminated by the kinetics of solid sintering and characteristic methods of XRD and FESEM.