Based on the classical dynamic theory of the cable and Euler beam as well as the dynamic equilibrium conditions at the joint of cable and beam, the in?plane vibration theory of a multiple cable?stayed beam was established, in order to study the couple vibration between cables and bridge deck. The combined effects of nonlinear terms due to the cable′s geometry were considered, and the beam was separated into some segments. Using a double?cable?stayed beam model as an example, the variable separation approach and boundary conditions were considered to solve the eigenvalue problem of the in?plane free vibration of a double?cable?stayed beam structure.Meanwhile, a finite element model of the double?cable?stayed beam was also developed to verify the proposed theory and method, and a well match of the results between the two methods was obtained. Finally, the analysis about the key parameters was conducted, and a comparison was made between the early outcomes of project group and this paper. It shows that the CFRP cables can improve fundamental dynamic properties of the system than the traditional steel cables. Increasing the axial rigidity of cable and the flexural rigidity of the beam can, respectively, obviously enhance the lower and higher frequencies of the model.