This paper describes a terahertz metasurface biosensor with a graphene and metallic aluminum composite structure. The aluminum structure is designed to form an electromagnetically induced transparency-like resonance. A layer of wet graphene is transferred onto the structure. The Fermi energy level of the graphene is controlled by the incorporation of silk proteins into the graphene, which causes the amplitude of the sensor's transmission spectrum to change. The experiment reveals that the detection limit is 0.35 ng/mL. The sensor is analyzed using the electromagnetic wave regulation characteristics of the Dirac point of graphene, as well as the coupling model. This biosensor enables the highly sensitive detection of trace proteins in the biomedical field.