The invention relates to the field of oil gas drilling and particularly relates to an application of amino acid modified graphene oxide in water-base drilling fluid as a coating agent. A preparation method for the amino acid modified graphene oxide comprises the step of subjecting graphene oxide and amino acid to a contact reaction in a water containing solvent in the presence of an alkaline compound. According to the application, the amino acid modified graphene oxide is a flexible laminar material and can be used for forming large-area adsorbed filling on the surface of shale as a coating agent so as to efficiently block off nano pores; and better performance of inhibiting clay swelling and shale dispersing can be achieved in a low concentration.