Ultra-high pressure sintering is sintering under higher pressure conditions. Due to the higher pressure, the diffusion of atoms is inhibited and the nucleation barrier is relatively small. Therefore, high density (>98%6) can be obtained at lower temperatures High purity alumina ceramics. In the process of ultra-high pressure sintering, the presence of pressure increases the vacancy and atomic diffusion rate in the particles. The pressure and surface energy together act as the driving force for sintering to enhance the diffusion effect. Ultra-high pressure sintering usually only needs to be carried out at a relatively low temperature. The abnormal growth of crystal grains is suppressed, so as to obtain high-purity alumina ceramics with high densification, fine subaluminum grain size and uniform distribution.