The invention discloses a preparation method of a graphene oxide reinforced leather solid waste collagen powder/polylactic acid composite. The preparation method is characterized in that graphene oxide, sodium hydroxide, sodium chloroacetate and water are mixed for reaction, filtered and washed to obtain surface modified graphene oxide; leather solid waste collagen powder is mixed with water, glutaraldehyde is added, pH is regulated to be 8.0 through sodium bicarbonate, the mixture is filtered, solid substances are washed and dried, and hydrophobic leather solid waste collagen powder is obtained; 1-100 parts by weight of the hydrophobic leather solid waste collagen powder, 1-100 parts by weight of polylactic acid, 1-20 parts by weight of the surface modified graphene oxide, 0-10 parts by weight of a compatibilizer and 0-10 parts by weight of a plasticizer are taken and mixed, the uniformly mixed co-mixture is dried and fed into a twin-screw extruder for melt blending, extruding and granulating, and the composite is prepared. The composite has excellent thermoplastic processing characteristics and mechanical properties, and a product of the composite can be degraded completely after use and is environment-friendly.