The invention discloses a preparing method for a graphene/titanium dioxide photocatalyst. A graphene/titanium dioxide nanometer composite is prepared from single-layer graphene and nanometer titanium dioxide particles, wherein the nanometer titanium dioxide particles are dispersed on the surface of graphene and are anatase type crystals. The catalyst prepared through the method has a high specific surface area, a high adsorption property and high photocatalytic activity, and is capable of effectively removing VOC gas. The degradation efficiency of the graphene/titanium dioxide photocatalyst prepared through the method on acetone reaches 85% within 1 h under an ultraviolet lamp.