Abstract: The vibration modes of flexible hanger rods in tied arch bridges are obtained from the deflection curves of the bridge under uniformly distributed load and restrained by different boundary conditions. Then, the paper derives the relationship between the tension of anchor wire, bending rigidity and natural frequency of the hanger rod. Thus, the measurement formula of the first 2 natural frequencies of the hanger rod can be obtained using Rayleigh energy method. This formula treats the flexural rigidity as an implicit calculation parameter, so that the difficulty in indentifying it is avoided. Finally, the calculation results are compared with the measured results, demonstrating that the proposed formula meets the requirements of tension measurement of hanger rods during construction and operation.