The structural dynamic characters of rotor and tower of horizontal axis wind turbine were analyzed. Because of the slender shaft structure, the rotor and tower were considered as a cantilever and two-node beam element was applied for discretization modeling. The motion equation was set up based on Multi-DOF Lagrange equations in the generalized coordinate system. The modal analysis was used to get natural frequencies and mode shapes, and Newmark method was used to determine the dynamic response under load. As an example, a 1.5MW wind turbine was calculated and the deviation displacement of this wind turbine was obtained by organizing the MATLAB simulation program.