The high-pressure α-PbO ₂phase of TiO ₂has suitable band gap and photocatalytic capability in the visible light range, which is an environmentally friendly and efficient photocatalytic material. In this work, α-PbO ₂phase of TiO ₂is obtained by the pressure-relief treatment of anatase nanospheres through using diamond anvil cell, and transmission electron microscope (TEM) observation shows the obvious deformation of TiO ₂nanospheres. High-esolution TEM shows that there are a large number of stacking faults along the [100] direction and deformation twins in the grain. Specifically, the deformation twin band with lens lamellar structure is formed in the submicron grain. The fan-shaped multiple deformation twins are formed in the nanocrystalline grains. This study shows that anatase TiO ₂can be deformed under high pressure, and its micro mechanism of deformation is similar to metal’s, mainly including deformation twins and stacking fault slip. There is obvious size effect in the formation of deformation twins. These results provide a new breakthrough point for the study of the size effect of high-pressure phase transformation of TiO ₂, and also point out an experimental direction for preparing the twin high-pressure α-PbO ₂phase.