The frequencies of concrete beam strengthened with fiber-reinforced polymer have been studied by using finite element method. Based on Mindlin shear deformation theory, the mass matrix and the stiffness matrix of concrete beam, adhesive element and composite laminates have been constructed. By typical numerical results, the natural frequencies of free vibration for concrete beam reinforced with FRP have been achieved and the method used in this paper will provide a reference for study dynamic characteristics of concrete structures strengthened by FRP.