The nonlinear dynamics of the cablestayed arch under cables subjected to external excitation was investigated.The coupling nonlinear dynamics equations of the cablestayed arch derived by using Hamilton principle were used.First,the Galerkin method was used to discrete the nonlinear equation of planar motion.Then the method of multiple scales was applied to perturb the discrete equations of motion,and the averaged equation under the primary resonances of cables was obtained.The impact of the vibration of cables over the vibration of arch under cables subjected to external excitation was studied,and the equilibrium solution,the period solution and chaotic solution of averaging equations were examined.The analysis results indicate that the internal resonance of the cablestayed arch possibly appears when the frequency of cables approaches close to the frequency of arch,the energy is transferred mutually between cables and arch,and the cablestayed arch presents complicated nonlinear dynamics behavior such as leap,bifurcation and chaos within the resonance frequency region.