The invention discloses a preparation method of a phosphotungstic acid doped titanium dioxide photocatalyst. The preparation method comprises the steps: firstly, dropwise adding a certain amount of butyl titanate into absolute ethanol to make butyl titanate uniformly dispersed, dropwise adding a small deal of acetic acid and triethanolamine, and carrying out stirring and standing to obtain a liquid marked as a liquid A; then, adding a certain amount of absolute ethanol into a small deal of mixed solution of distilled water and acetic acid, and carrying out stirring and standing to obtain a liquid marked as a liquid B; secondly, slowly dropwise adding the liquid B into the liquid A, slowly dropwise adding a certain amount of phosphotungstic acid solution into the mixed solution, firstly, carrying out magnetic stirring to uniformly disperse the solution, and then, carrying out ultrasonic treatment for 30-50min to obtain a uniform, transparent and white sol; and finally, carrying out ageing, drying, heat treatment and grinding on the sol to obtain a light gray phosphotungstic acid doped titanium dioxide powder. By using the preparation method, the problem that a method for doping phosphotungstic acid into titanium dioxide is relatively complex in step and relatively high in energy consumption in the prior art is solved.