The invention discloses a preparation method of graphene organic size. The preparation method includes: utilizing a graphene oxide water solution as a raw material; subjecting the raw material and an organic solvent with a dispersant dissolved in to liquid-liquid mixing and homogenizing; removing water in the solvent while performing reduction to obtain the graphene organic size. Conventional ideas are broken through, high dispersity of GO (graphene oxide) in water is utilized to bring a non-stacked state of GO in water into an organic phase, reduction of graphene oxide is realized synchronously in the process of solvent replacement, and finally the graphene organic size which is high in concentration and dispersity can be obtained; process design is ingenious, and production cost can be lowered effectively. In addition, content of graphene in the graphene organic size obtained by the preparation method can reach higher than 0.05wt%, and the graphene organic size does not settle after being placed at normal temperature for 30 days. Graphene oxide is reduced in the process of heating, distilling and dewatering, in this case, graphene is heated uniformly, and reductive effect is better at same temperature; under a heating condition of 150 DEG C, reductive degree can reach below 20wt% in oxygen content.