The invention relates to a preparation method of a titanium dioxide loaded palladium-zinc cadmium sulfate photocatalyst. The method comprises the following steps: (1) after dissolving Cd(NO3)2 into absolute ethyl alcohol, adding a NaOH solution and hydrazine hydrate and transferring the mixture into a reaction kettle; after reacting, obtaining a reaction solution; (2) after heating the reaction solution, adding Zn(NO3)2 to obtain a mixed solution; (3) dissolving (NH4)2S into the absolute ethyl alcohol and dropwise adding into the mixed solution; after stirring, centrifuging and drying to obtain ZnCdS; (4) ultrasonically dispersing the ZnCdS and bi(2,4-pentanedione)palladium into de-ionized water to obtain a yellow turbid solution; (5) adding glacial acetic acid and tetrabutyl titanate into an ethylene glycol solution; stirring in an ice water bath to obtain colorless transparent liquid; (6) dropwise adding the yellow turbid solution into the colorless transparent liquid and then adding de-ionized water; stirring to obtain a blackish green turbid solution; (7) transferring the blackish green turbid solution into the reaction kettle and reacting; centrifuging to obtain a blackish green solid; (8) washing, centrifuging and drying the blackish green solid to obtain the titanium dioxide loaded palladium-zinc cadmium sulfate photocatalyst. The method provided by the invention is simple and is low in cost.