This paper presents a fundamental study of a structural health monitoring technique called the piezo-impedance method, which utilizes an electromechanical property of piezoceramics. For a thin beam with tensile force, an analytical model of the piezo-impedance method is formulated based on the wave propagation theory. Also, a tensile force identification method in a thin beam combined with optimization techniques is proposed. An experiment is performed with small test pieces of a beam to investigate the validity of the proposed method and it is found that analytical results are in good agreement with experimental measurement results and that the tensile force is identified with accuracy. By using the proposed method, it is possible to identify absolute value of the tensile force in a beam from only one measurement.