From the frequency characteristic equation of a beam fixed and hinged at both ends, the frequency relationship between the two states was discovered, and a simple practical formula in the estimation of cable tension was proposed, which has definite physical meanings. The results from case studies have demonstrated that the formula can simulate the tension condition precisely for cables, so it can be used to identify the tension of cables with different slenderness ratios and flexural stiffness more easily and accurately. The influence of different cable boundary conditions on the cable tension calculation results was analyzed, and a cable tension formula which can take into account the rotational stiffness of the cable ends was proposed.