Based on the dynamic theory of taut string and Euler beam as well as the dynamic equilibrium conditions at the joint of cable and beam, the in-plane free vibration theory of a cable-stayed beam was established. The transfer matrix method and boundary conditions were considered to solve the eigenvalue problem of the in-plane free vibration of a cable-stayed beam structure. Meanwhile, a finite element model of the cable-stayed beam was also developed to verify the proposed theory and method. he predictions by the proposed method match well with those of the finite element analysis. Finally, the parametric analysis was conducted, which shows that the fundamental dynamic properties of the cable-stayed beam are improved by replacing steel cables with CFRP cables.