Abstract: In order to prevent the drilling fluid filtrate from entering the formation, to maintain the wellbore stability and to protect the reservoir, a procedure to activate a graphene surface was conducted by using a modified Hummers method. It introduced carboxyl, hydroxyl, epoxy groups and other active groups, resulting in a kind of graphene modified film-forming agent SMSL with ultra-low permeability. It was prepared by grafting copolymerization with selected monomers on the surface of active graphene. The molecular structure, micro morphology and dispersive state of SMSL were analyzed by the infrared spectrometer, the element analyzer, the atomic force microscope and the synchronous thermal analyzer. Researchers used pressure transfer tests, core self-seepage tests and SEM to evaluate the dense film-forming plugging characteristics of SMSL and the compatibility of SMSL with the water-based drilling fluid. The results showed that the molecular structure of SMSL met the design requirements, and it could significantly reduce the pressure transfer and self-seepage effect of rocks. Specifically, the shale film-forming efficiency was 162.96% higher than that of the conventional polymer film-forming agent, the self-seepage capacity of tight sandstone was decreased by 88.74%, with very good compatibility with the water-based drilling fluid. The research indicated that when SMSL was added into the drilling fluid, a dense film can form on the wellbore to prevent the filtrate from entering the formation and thus can maintain wellbore stability and protect the reservoir.