This paper studies nonlinear dynamic behavior of a stringbeam coupled system subjected to parametric and external excitations. Firstly, the method of multiple scales is used to analyze the nonlinear responses of the string-beam system coupled system. Secondly, based on the average equation and taking the damping coefficient of the system as the bifurcation parameter, the stability of the equilibrium point of the system is analyzed and the bifurcation curve of the equilibrium point is obtained. In order to verify the correctness of theoretical prediction, the trajectories in phase space under different bifurcation parameters are simulated. Finally, the fourth-order Runge-Kutta method is utilized to verify the existence of the chaotic motions in the stringbeam coupled system. From the results of numerical simulation, it is clearly found that the system exists period-1 motion, multi-periodic motion and chaotic motion.