In this paper,the Fourier spectrum-based strain energy damage detection method for beam-like structures is proposed based on the discrete Fourier transform.The classical strain energy damage detection method localizes damage by the comparison of the strain energy between the intact and inspected structures.The evaluation of the 2nd-order derivative term in the strain energy plays a crucial part in the comparison.The classical methods are mostly based on a numerical derivative estimation for this term.The numerical derivative,however,introduces additional disturbances into damage indications.To address this problem,a discrete Fourier transform-based strain energy is proposed with the emphasis of enhancing the performance in noisy condition.The validations conducted on the simulated and experimental data show that the developed method is effective enough for composite beam damage detection in noisy environments. In this paper, the Fourier spectrum-based strain energy damage detection method for beam-like structures is proposed based on the discrete Fourier transform. The classical strain energy damage detection method localizes damage by the comparison of the strain energy between the intact and inspected structures The evaluation of the 2nd-order derivative term in the strain energy plays a crucial part in the comparison. Classical methods are mostly based on a numerical derivative estimation for this term. Numerical points, however, introduces additional disturbances into damage indications. To address this problem, a discrete Fourier transform-based strain energy is proposed with the emphasis of enhancing the performance in noisy condition. The validations conducted on the simulated and experimental data show that the developed method is effective enough for composite beam damage detection in noisy environments.