By using FEM method, the natural frequencies of the super-long steel and CFRP cables with possible engineering parameters have been comprehensively studied. The error and limitations of cables’ natural frequencies theoretical calculation formula have also been analyzed. The results show that: Theoretical formula results are more approximate to out-plane frequencies of the cables. In a symmetric mode, out-plane frequency is lower than in-plane frequency, whereas in an asymmetric mode the situation is reversed. The difference between out and in-plane frequencies appear most in the first-order mode. The difference between out and in-plane frequencies is more obvious for cables with low stress, small inclined angle, long length with big sag and strong nonlinearities. The nonlinearities of CFRP cable is relatively slight for its lightweight and high strength. Out and in-plane frequencies are almost identical, and the theoretical formula is applicable to CFRP cables.