The modal calculation and analysis method as well as the effect of the rotational speed on the natural frequency, for the large?scale wind turbine blade in static and variable speed running conditions were studied. In this paper, the finite element model (FEM) of wind turbine blade was also established. The coupling loading method was applied during stationary analysis. Lanczos method was used to analyze the modes of the blade. The effect of the pre?stressing on the natural frequency and the stability performance of the blade were investigated. Meanwhile, the effect of rotational speed on the natural frequency was discussed. The reason of the pres-tressing effect was also analyzed. The results showed that the modes of vibration were mainly flap?wise and edgewise motion for the wind turbine blade, and the pre?stressing effect has a significant effect on the natural frequency, where the natural frequency of the blade was also increased with the increasing rotational speed. Furthermore, the effect of pre?stressing effect on the flap?wise stiffness was greater than that of edgewise stiffness.