The invention belongs to the field of oil sand tailings flocculation, and discloses a preparation method of a graphene/titanium dioxide/polyacrylamide composite self-degradation flocculating agent. The method comprises the steps that oxidized graphene is prepared through a Hummers method; oxidized graphene/titanium dioxide gel powder is prepared through a sol-gel method, the oxidized graphene/titanium dioxide gel powder is subjected to heat treatment in inert atmosphere, and graphene/titanium dioxide is obtained; the graphene/titanium dioxide and an acetone-water solution of acrylamide are placed in a quartz tube, ultraviolet irradiation, centrifugation, washing and drying are carried out, and the graphene/titanium dioxide/polyacrylamide composite self-degradation flocculating agent is obtained. According to the flocculating agent, the characteristic that a polyacrylamide polymer chain is prone to winding can be overcome, a comb type structure is formed on the surface of graphene/titanium dioxide, therefore, the polymer chain is well expanded, the flocculating effect is good, and self degradation can be carried out under the condition of light.