The dynamic characteristics of an assumed isolated CFRP main cable are studied. The section area of the CFRP cable is determined for suspension bridge in different spans and sag-span ratios based on the principle of limit design at a given security coefficient. The Irvine parameter for suspension bridge with backstay and without backstay is calculated and a rule that Irvine parameter is linearly changed with span and sag ratio respectively is found. The analysis of frequency change with span shows that the first and third symmetric frequency is lager and less than the corresponding antisymmetric frequency respectively, but the second symmetric and antisymmetric frequencies are close to each other. The analysis on frequency and dimensionless frequency change with sag ratio show that for bridge with and without backstay the first and third order symmetric frequencies are larger and less than the corresponding antisymmetric frequencies respectively, but for a bridge without backstay the crossover phenomenon happens and the second symmetric mode changes from two to four internal nodes mode.