Abstract: Taking natural flake graphite as a raw material, nano-graphene oxide(GO) as a high performance fluid loss additive was prepared by means of the modified Hummers' method. The chemical structure and micro-topography of GO were characterized through a combination of FTIR, XRD, TG and TEM. The performance of GO on fluid loss control was evaluated via an API filtration tests and a comparison of GO with several commonly used fluid loss additives was made. The results shows that: GO performances much better in reducing fluid loss than other additives even at relatively low concentration due to its good aqueous dispersion of nano scales; it was found in a formulation experiment of GO with bentonite and carboxy methyl cellulose that GO is an outstanding plugging type fluid loss additive even in the absence of bentonite; in order to further improve the performance of reducing fluid loss at low cost, GO can be composited with some viscosifiers; the results of grain size analysis indicated that the bigger the transverse grain size, the better GO performances, therefore the key to prepare GO with large horizontal scale lies in taking low-mesh natural flake graphite as a raw material.