In order to exactly model the aeroelastic response of a blade under turbulent flow and study blade vibration's feedback on aerodynamic load and aeroelastic response, here a nonlinear aeroelastic mechanical model containing flexible blade multibody system's dynamic model and an aerodynamic model was constructed. Through discreting a flexible slender blade into a multi-rigid-body system, the aeroelastic coupled equations of the blade were obtained by using the theory of computational dynamics of multibody system and Roberson-Wittenburg modeling method. In the coupled equations, the blade element-momentum theory (BEM) was used to calculate the aeroelastic load of the wind turbine blade and Kaimal model was used to calculate random wind speed. The time domain response of a 5-MW offshore wind turbine blade of the US. Renewable Energy Laboratory was calculated. The response included the vibration of the blade and the flapwise and edgewise bending moments at the blade root. The effect of the vibration of the flexible blade on the aerodynamic load was also studied. The results revealed that the effect of slender blade vibration can not be ignored when simulating the aeroelastic response of a wind turbine.