Long span cable-stayed bridges usually use dense cable systems, and the vibration frequencies of cables are very close, and there may be a frequency doubling relationship between cables. Therefore, there may be mutual coupling vibration between cables. Cable is an important load-bearing component of cablestayed bridges, and it is very important to study the dynamic characteristics of multi cable single beam. In this paper, considering the boundary conditions of cable girder, cable tower and tower girder and the connection conditions at the connection points, based on Hamilton variational principle, the differential equations of motion of multi cable single beam structures are established. After dimensionless treatment, the reduced differential equation of motion is obtained according to the method of separating variables. In this paper, two adjacent cables are taken into account to analyze the dynamic behavior of double cable single beam coupling structure under different working conditions. It is found that, different from the "frequency turn" phenomenon in previous data, in this paper, the two frequency curves do not separate rapidly at the place where the frequency values are close, but continue to keep parallel and close to each other within a relatively small parameter range, and then separate rapidly. Finally, the nonlinear characteristics of the double cable single beam coupling structure are studied, and the structure is discretized with two degrees of freedom and one degree of freedom respectively. It is found that the single mode assumption of the structure can reflect the nonlinear characteristics of the structure in the non resonant region, but in the resonant region, the nonlinear characteristics of the structure will jump, so it is more accurate to apply the two degree of freedom mode theory to research.