Abstract: Aiming at the problem of dynamic analysis failure of ultra-long flexible wind turbine blades under traditional linear（small deformation） conditions, a flexible blade model with the large-deflection structure is developed to study the dynamic response. The blade is simplified as a cantilever and discretely modeled by applying the large-deflection model which is derived from the Euler-Bernoulli beam. Then,the nonlinear aeroelastic dynamics equations of the blade model are established by using blade element momentum（BEM）theory,and time-domain simulations are performed by using the nonlinear Newmark method and Newton-Raphson method. The changes of the structural stiffness and the pose of the blade are considered throughout the process. Finally,the nonlinear model is applied to the DTU 10 MW wind turbine. The results show that the large-deflection model significantly increases the flapwise deflection and torsion angle of the blade tip in dynamic response,while slightly reduce the edgewise deflection. Meawhile,the large-deflection model significantly reduces the flapwise load of the blade root in dynamic response,while slightly increase the edgewise load of the blade root,which is different from the result of the linear model.