Abstract: With the continuous increase in wind turbine size, the lengthening blades exhibit reduced rigidity, leading to enhanced structural flexibility. This "long-flexible" characteristic exacerbates the issue of significant blade vibrations, and nonlinear vibration analysis plays a crucial role in accurately assessing blade responses. Establishing precise dynamic models to analyze blade behavior is of paramount importance. In this study, based on the Euler-Bernoulli beam theory, a nonlinear dynamic model is developed for the NREL 5 MW wind turbine blade, incorporating degrees of freedom in both flapwise and edgewise directions. To improve the accuracy of blade response prediction, the present model accounts for orthogonal hub motions, including the resulting inertial excitations and aerodynamic loads. The influence of hub motion amplitude and yaw angle on the blade dynamic behavior is systematically analyzed. The results indicate that, under the same excitation amplitude, the peak value of the second mode is significantly higher than those of the first and third modes, with a much narrower bandwidth. Internal resonance occurs among the first, second, and third modes due to a harmonic relationship of their natural frequencies, leading to energy transfer among modes. Under operating conditions, the amplitude of the first mode response is highly sensitive to the yaw angle, increasing substantially as the yaw angle increases, while the second and third modes remain almost unaffected by the yaw angle. This study investigates the nonlinear vibrations and internal resonance characteristics of rotating blades, providing a critical theoretical basis for vibration suppression design and operational parameter optimization of large-scale wind turbine blades, offering significant insights for enhancing structural safety and economic performance.