The invention discloses a preparation method for a titanium dioxide porous microsphere. The preparation method comprises the following steps: dissolving cellulose triacetate and a precursor into a cosolvent to obtain a precursor blended solution; performing thermally induced phase separation on the precursor blended solution to obtain a cellulose triacetate/titanium dioxide composite porous microsphere; and hydrolyzing the cellulose triacetate/titanium dioxide composite porous microsphere in an alcohol solution of sodium hydroxide, and performing washing, drying and roasting successively to obtain the titanium dioxide porous microsphere. The preparation method has the beneficial effects that the TiO2 porous microsphere prepared by the preparation method consists of fibers which have diameters of 20-80 nm, and are outwards radiated from the center, so that the specific surface area of the porous microsphere is greatly improved. Multiple scattering is generated on a gas-solid interface, so that light obtaining is facilitated. Therefore, the preparation method is very suitable for being applied to the aspects of photocatalysis and working electrodes of solar cells.