The invention relates to a preparation method of TiO2 nanotubes modified by silver nanoparticles with different particle diameters, comprising the following steps of: ultrasonically dispersing spherical TiO2 particles into a sodium hydroxide water solution; increasing the temperature of the sodium hydroxide water solution of TiO2 to 150 DEG C, making the sodium hydroxide water solution react withthe TiO2 for 24 hours, and then naturally cooling; centrifuging the cooled sodium hydroxide water solution of the TiO2; dispersing the TiO2 cleaned and precipitated to be neutral into a salpeter solution of 0.1 mol/L to obtain the TiO2 nanotubes; dispersing the prepared TiO2 nanotubes into an organic solvent; adding an adsorbent to the organic solvent containing the TiO2 nanotubes; dispersing obtained yellowish TiO2 nanotube particles into the organic solvent, and dropwise adding an AgNO3 solution; annealing obtained TiO2 nanotube particles modified by silver quantum dots at different temperature in an inert atmosphere so that the silver quantum dots positioned on the surface of the TiO2 and in the TiO2 grow in a curing way; and cooling to obtain various TiO2 nanotubes modified by the silver nanoparticles with different particle diameters.