Dual-rotor wind turbine is a new type of horizontal axis wind turbine, which can use the wake of the front wind turbine to generate electricity and has a high utilization coefficient of wind energy. However, in order to reduce the flow field interference effect between the front and the rear wind turbine, the axial span of the transmission chain is longer than that of the single wind turbine, resulting in complex transmission chain modal characteristics and high potential resonance risk under the multi-point elastic support of the long-span flexible frame. In this paper, considering the frame flexibility and elastic support between the frame and the transmission chain, a rigid-flexible coupling dynamic model of the transmission chain of dual-rotor wind turbine was established, the coupling vibration mode of the transmission chain was analyzed, and the influence of frame flexibility on the inherent characteristics of the transmission chain was studied. The results show that the first two torsional vibration natural frequencies of the wind turbine transmission chain are 5.63Hz and 6.01Hz respectively, which correspond to the first torsional vibration natural frequencies of the rear and front wind turbine transmission chains respectively. There are three vibration modes in the drive chain of dual-rotor wind turbines, including the local vibration mode of the front or rear wind turbine drive chain, the coupled vibration mode of the front or rear wind turbine drive chain and the coupled vibration mode of the front and rear wind turbine drive chain. When the modal energy of each component of the system is mainly concentrated in the non-torsional direction, the frame flexibility will make the modal energy of each component transfer to the other components of the same side drive chain or the other side drive chain components.