The invention discloses a preparation method of a graphene quantum dot-graphene-titanium dioxide composite material, and belongs to the technical field of nanometer material preparation. The preparation method comprises the steps that firstly, a graphene-titanium dioxide nanotube composite material is prepared from graphite oxide and titanium dioxide; secondly, a nitrogen-sulfur-doped graphene quantum dot solution is prepared from citric acid and thiourea in DMF; lastly, the graphene-titanium dioxide nanotube composite material and the nitrogen-sulfur-doped graphene quantum dot solution are mixed, stirred for 24 hours away from light, centrifugally separated and dried, and then the graphene quantum dot-graphene-titanium dioxide composite material is obtained. The composite material prepared through the method has the excellent catalytic performance and can degrade dye under the visible light condition, the photocatalytic efficiency is obviously improved compared with an original material, the environmental friendliness is achieved, no heavy metal ion can be introduced, and no secondary pollution can be caused to the treated water resource.