The invention relates to a method for preparing a graphene biosensor, belonging to the technical field of electrochemistry. The method comprises the following steps of: immersing a processed gold electrode into graphene oxide and a sodium sulphate solution, electrically depositing the electrode through a control electric potential, taking out the electrode, washing the electrode by using water, after drying the electrode at room temperature, putting the electrode in a chloroauric acid solution, electrically depositing the electrode through the control electric potential, taking out the electrode, washing the electrode by using water, and drying the electrode at room temperature; putting a modified electrode in a conductive polymer monomer and a supporting electrolyte solution, polymerizing the electrode through the control electric potential by adopting a cyclic voltammetry, taking out the electrode, washing the electrode by using water, and drying the electrode at room temperature; and activating the modified electrode in an EDC/NHS (Dichloroethane/N-Hydroxysuccinimide) solution, and immersing the modified electrode in a vomiting toxin antibody. The method disclosed by the invention is used for fixing graphene, gold nanoparticles and conducting polymers through electro-deposition; therefore, the method is very green and environment-friendly; furthermore, the thickness of a coating and sizes and distribution densities of the gold nanoparticles can be precisely controlled, thus, the batch production repeatability of the modified electrode is good.