Considering the initial configuration and support stiffness of cable-stayed bridge，the multi-cable-stayed shallow-arch model with vertical elastic constraints is established. Firstly，based on the classical dynamics equations of the cable and shallow arch，the theory of in-plane free vibration of the model is deduced by dividing the shallow arch into several segments at the cable-arch coupling points. Then，the double-cable-stayed shallow-arch model is taken as an example and its in-plane eigenvalue problem is solved by separation-of-variable method. At the same time，taking the double-cable-shallow arch model as an example，the corresponding finite element model is established. The frequencies and mode shapes calculated by the present method are compared with those obtained by finite element method，which verifies the correctness of the method and model in this paper. Finally，a systematic parametric analysis on the dynamics properties of the model is conducted. It is shown that the vertical stiffness has a significant effect on the dynamics properties of the system.